You're both correct. Most everything is on SC21, with VHF used as a fill in. If I remember right they can and sometimes do simulcast dispatch side only onto VHF, at least from the tower on the north side of Augusta. Sheriff can be heard on all the SC21 sites within Hancock County, although the Augusta site tended to have slightly less traffic than Warsaw and Niota the last few times I was down there - it's all about which site the radios affiliate with. And then some fire agencies - Tri-County FPD for one - still use 155.415 for dispatch.
They've been using SC21 to one degree or another for about a year now, but they were using both like I said. Talking to my contact out there though she reports they're not on VHF anymore in her part of the county either so they must've finished upgrading everyone and switched over full time.
There has been gradually less traffic on VHF since they switched over to STARCOM. I heard traffic on VHF as recently as the past two weeks, but yes, most primary traffic, if you want to hear everything, is on STARCOM.