Not clear what is meant by "Compliance." Sounds like you are conflating the pistol list with the AWB compliance changes commonly made to semi-auto rifles.
These are separate things. The pistol list and "compliance" applies to dealers and you can buy "non MA-compliant firearms" (read "off-list pistols") from a LTC holder private party that hasn't done more than four this year (keeping in mind the mag capacity considerations, which are technically separate). Being a LEO gives it no special blessing, other than it's arguably easier for them to acquire those items.
As for rifles, depending on the circumstances, in my opinion/risk assessment, as a non-lawyer:
1.) Manufactured/Acquired/FA-10'd pre 7/20, meets the "old AWB" compliance standards - Sure.
2.) Manufactured/Acquired/FA-10'd post 7/20 (and assuming seller is original owner), meets the "old AWB" compliance standards - I wouldn't, but I bet a lot of people would.
3.) Manufactured/Acquired/FA-10'd post 7/20, does not meet the "old AWB" compliance standards - I'd rather not go to prison.
4.) Manufactured/Acquired/FA-10'd pre 9/1994 (pre Federal AWB), has all the good stuff (evil features) - Sure.