The letter you cite from the Lancaster Co., VA record book has been common knowledge for 100 years.Evidently it's a new discovery for you.
Grocers in Tudor and Stuart England were second in precedence among the trades.They were indeed well esteemed, but were entitled to nothing as far as potential wives are concerned.The Dale family was at the bottom of the social scale of those who were allowed to "bear arms."
I'm not a Carter descendant, so Capt. Thomas Carter's parentage right or wrong has no practical value for me.However, I think you are correct that Carter was of the mercantile class.Given what we know about Maj. Edward Dale's background, it's likely that the friendship between Carter and Dale had something to do with the their shared social class.
Both Dale and Carter were well educated, which implies relatively affluent backgrounds.But Thomas Carter was apparently not himself a lineal descendant of someone who was granted arms, which explains his (illegal) use of the Dale arms, I suppose in right of his wife.