Hi flipster
If nobody knows the answer to this , I can try and have a check around for you if you want , and if you are no rush to get the info.
My father-in-law has lived around the Glais area since the 1960's, my husband used to play rugby for Glais village and knows the area quite well too. And I think my mum-in-law studied some sort of history on the area for some sort of qualification ( something to do with teaching)
I don't talk to the in-laws every week ( phone bills!

I'm in Australia) , but if nobody can answer you, I'll ask them if they have heard of it next time I talk to them (which may be next week, or the week after etc) . Hubby may know too, or may have heard of it if it's still there, I'll ask him when he gets back. Whether they have ever heard of this building is another matter - I can only but ask them.
My own opinion, it may not be there, but touch wood it is; there has been some development going on in that area, some new houses popping up, and plus some of the old terraced/cottage homes have been knocked down and replaced with new in recent years ( it's cheaper to knock down an old house than renovate it attitude

) .
Glais is a small lovely old village, recently they have been building things there ( was in the area a few months back ) , spoiling the place if you ask me - such a shame. It still has plenty of old buildings. more old than new , and still has an old village feel/look, but if they carry on, it will be just another faceless suburb.
Here are a few old photo's here of some of the buildings in Glais:
http://www.page-net.com/swansea.localhistory/llansamlet/gallery/buildings/start.htmlFor the Homeguard if you're taking about the Glais area homeguards, and not Swansea town/city itself, it may be well worth looking at Birchgrove Homeguard too ( which is right next to Glais and a bigger area than Glais village) and also the Llansamlet Home guard too. He may have been in one of those too . I don't know if Glais had it's very own Homeguard , and there is a good chance he may have been in the Birchgrove one if you can't find him in the Glais( Birchgrove and Glais are close neighbours) and LLansamlet is the wider area, who are also their neighbours today ( once upon a time Llansamlet covered a huge area and covered places like Birchgrove etc). So it's worth bearing in mind these two neighbours as well in your research, Birchgrove and Llansamlet
From the same site , there are a few old photos of the various people in some of the homeguards of Birchgrove and Llansamlet
http://www.page-net.com/swansea.localhistory/llansamlet/gallery/people/start.htmlBest wishes

P.S Your G Uncle would have seen the German raids and devastation in Swansea town itself, and may have seen the odd "stray" bombing there in Llansamlet/Birchgove/Glais/ - also the near by areas/towns of Ynystawe, clydach etc
Funny place to be evacuated to- Swansea, but it seems your family moved there with work. Glais village where they were living , would have been a lot safer compared to the city/town of swansea.
You are right in your thinking he would not have been safe in the main Swansea area/town ( Swansea being one of the major ports in the UK was bombed like hell during WW2) - Swansea town and docks mostly got bombed- parts of swansea town were really flattened, and many people lost their lives in the bombings there.
My father-in-law as a child ( who is originally from Swansea town area, and lived near the dock area as a child ) got evacuated to a farm in Carmathenshire as a child in WW2 with his siblings and mum. It didn't really touch places like Glais all that badly like it did the town of Swansea , although looking at that site - Frederick place got a hit by the looks of things - that's in the Llansamlet/Trallwn area and not Glais( the Germans were more interested in bombing the port and the city of swansea, and that is where they did the most damage) , the people there in Glais, Birchgrove, Llansamlet etc etc would have been relatively "safe" ( well as safe as you can be when then is planes flying overhead dropping their bombs if you know what I mean

compared to the people in the main town area of Swansea and dock area.
I think they in the town and docks even evacuated some people/children into Mumbles ( which I find is really odd if you see how close Mumbles is to Swansea) from the town city of Swansea. I also find odd Mumbles wasn't bombed/flattened , as that is on the water too just little a hop and a skip away from the main town of swansea ( where my mum-in-law is from). No bombs fell on Mumbles at all to my knowledge - Hubby's grandfather was in the Mumbles homeguard as he was working for the electricity company at the time ,and I don't think he ever mentioned any bombs falling there and doing major damage , and I know mum-in-law and all her siblings as a children were not evacuated from Mumbles to a "safer" place.
I can't answer you on service records for the homeguards, maybe the Army will have them, . There maybe also be some sort of history for the homeguards in the Swansea archives. (?)
Anyway, If nobody has heard or knows of this " Brynterian House" ,I can ask the inlaws next time I talk to them, perhaps they have heard of it,or know of it, and will know if it is still there today.