According to Dave Meltzer on the latest Wrestling Observer Radio, Finn Balor is still making the same downside guarantee he agreed to on the main roster. While he likely won't be making much in terms of bonus payouts now that he's on NXT, this is obviously a good deal for the former Universal Champion.
Whether he'll still be paid like a main roster talent when it comes time to sign a new deal is hard to say, but Balor is a top star on NXT and a big draw in the Wednesday Night War with All Elite Wrestling.
NXT Women's Champion Rhea Ripley is a slightly different case, though, because even though she's part of NXT, she's currently appearing on RAW ahead of her match with Charlotte Flair at WrestleMania. While she still has an NXT contract, Ripley is likely receiving bonuses for RAW, and should score a nice payday for the Show of Shows.
The hope is that NXT's move to the USA Network will mean Superstars from that brand will start getting paid more, so hopefully that's something which is also going to be the case moving forward.