just to note that I managed to do this following a suggestion (thank you!) to use textsplit():

=AND(ISNUMBER(VALUE(FIND(MID(TEXTSPLIT(A1,",",,TRUE),1,1),"ABCDEFGHIJKLMNOPQRSTUVWXYZ",1))),ISNUMBER(VALUE(FIND(MID(TEXTSPLIT(A1,",",,TRUE),2,1),"ABCDEFGHIJKLMNOPQRSTUVWXYZ",1))),ISNUMBER(VALUE(MID(TEXTSPLIT(A1,",",,TRUE),3,8))),LEN(TEXTSPLIT(A1,",",,TRUE))=10)

Posting this in case it's useful to anyone else. If the "ABCDEFGHIJKLMNOPQRSTUVWXYZ" makes this formula too long for custom data validation (255 character limit) put that in a cell and refer to it in the formula. Note this doesn't enforce uniqueness, that's been a step too far for me thus far!