I couldnt find a marriage of a William Webb to an Agnes Harper, so either his real name was one of those on the marriage that Suttontrust found, or they never actually married.
If William Webb was a stage name that he used at that particular time, or a name he used when with Agnes (other thread says he left her) and there are no other records that can be found in that name (which seems to be the case) then it is going to be very difficult to find out anything more about him, as we dont know what name(s) he used at other times.
We dont know if he was a actor performing at a theatre in a stage play, or something far more casual of a travelling kind. It is really pointless (though fun!) to try and guess anything.
The only leads at present, as I see it, are this census entry, the children's births, and that possible marriage of an Agnes Harper that was found.
So, if you want to explore every angle before giving this up as a lost cause, they are all that can be pursued.
First the census - that doesnt give us a lot to pursue. IF he was truthful about his age and place of birth then we can see if there are any 30 yr old actors born Beverly in 1881, for example, as a next step.
Then the children - what does Margaret's birth cert say? Is dad described as an actor then? Is mother Webb nee Harper, no other names? Does address give any clues as to what sort of place they were at? et etc
Then there is Violet, we could look for her and see if her cert brings any clues.
And of course there is 1911, have you found Margaret on there? Or William or Agnes? that would probably be the best next move for you.
I am doubtful you will get anywhere with this, but you really never know. That's the thing with this sort of research, you just never know where or when a lead will take you to the vital piece of info that makes it all fall into place,. Often you can follow hundreds without getting anywhere, but personally I never give up, and that has paid its dividends on occasions!