I think Gridle (Santeri) is probably still on the mamedev list. He was never really active with any sort of mame development. I'm not really sure how he got there tbh. Moogly Guy is active, he's the guy who made the HLSL effects stuff in mame. Also known as Just Desserts and other aliases such as Harmony. He's banned from here for acting like he did on mame.net. On mame.net if you programmed mame you could do whatever you wanted. There were a bunch of active devs back then that posted there for a period. Most are no longer active.