I believe your sales rep is right. I think I have heard that discussed on this forum before but can't find the link to that discussion.
I think that a builder can stipulate this
ON A NEW HOME if they want to. There may be too many hoops to jump through with a VA loan that the developers don't want to deal with. They have no problem selling homes.
Resales are entirely a different issue.
Here is a similar discussion on Zillow.
Can a new home builder refuse to allow a VA loan in a new development if they are approved VA/FHA? - Zillow Mortgage Advice
EDITED. Found an earlier discussion on this subject on this forum.
VA Loan Certificate In Process