A whole lot of folks who were mortal when they learned their arts, and joined the Anarchs to continue practicing those arts in relative peace. And their students, of course. I suspect the "Old Skool", in response to the filthy Tremere Usurpers coming in and trying to establish themselves in the Anarchs, would start taking a bunch of new apprentices, just to combat that incursion. And I am suspicious of any suggestion that these blood magicians would be happy about letting Tremere join their ranks. Putting aside the ever-present fear that these "Anarch Tremere" are just double agents for the Pyramid, Clan Tremere is a large part of why Old Skool blood sorcerers have to collect among the Anarchs in the first place. That old priest of Apollo might have been a respected elder in his day, before the Warlocks came and cast doubts on the safety of his traditional devotions.
That's not even getting into the fact that a lot of the Hackavist blood sorcerers are Tremere "defectors". Tremere with their newfangled techno-toys. I don't see traditionalists having a high opinion of these modern sorceries. That drives a wedge between the two factions even further.