Does the FHA or VA have servicing transfer requirements that require letters to be sent ahead of time?

You mean over and above those required by RESPA?

Yes, I find that VA guidelines refers to RESPA but I was wondering if you could help advise on the FHA piece.

FHA: https://ecfr.io/Title-24/Section-203.508

Same there.

"(e) Each servicer of a mortgage shall deliver to the mortgagor a written notice of any assignment, sale, or transfer of the servicing of the mortgage. The notice must be sent in accordance with the provisions of § 3500.21(e)(1) of this title and shall contain the information required by § 3500.21(e)(2) of this title. Servicers must respond to mortgagor inquiries pertaining to the transfer of servicing in accordance with § 3500.21(f) of this title."

Of course those cross references to part 3500 go nowhere now. Essentially they refer to the transfer notices included in Reg X section 1024.33, I believe.