Thrapston is in Northamptonshire, so doesn't appear in the 1841 Hunts census set. You might also consider posting on the Northants board. So the member submission on the IGI was wrong when it stated that they married in Old Weston Hunts? What was the date of the marriage in 1841?
The absence of a father's name usually signifies illegitimacy, although it has been known for the bridegroom not to give a father's name if he knows that the bride was illegitimate, in order to save her possible embarrassment.
Since we last exchanged messages in September the 1861 has been indexed and is online.
RG9/981 folio 83
Ramsey, Hunts
William Oliver head marr 60 brick maker b Castor Northants
Harriet Oliver wife 38 b Winwick Northants
Pryor Gray son in law (=stepson) 14 b Alconbury Hunts
Amelia Gray dau in law (=step dau) 12 b Alconbury
William John Gray son in law 10 scholar b Alconbury
Alfred Gray son in law 8 scholar b Alconbury
Harriet Oliver dau 1 b Ramsey Hunts
Hoods Ferry, March, Cambs
Reuben Gray lodger unmarr 15 ag lab b Alconbury
in the household of James Driver 33 and family plus three other lodgers, all ag labs.
It is also the Alconbury 1851 that you need as the Greys' children were born there. Unfortunately it hasn't been released on CDRom, but perhaps someone reading this may have the Hunts FHS transcript. Alternatively there are people offering Alconbury look ups for 1851 on the Huntingdonshire look up exchange on
http://members.tripod.com/AztecRose/huntingdon/hun.htmlRegards
David