The Wiki says that slime spawning was broken sometime after Alpha v1.0.17 (exact version unknown) until Beta 1.2_01, so it sounds like they either only spawn in very limited areas (conditions unknown) or not at all in Alpha 1.1.2_01 (if "disabled" means that they completely disabled it, as opposed to just being broken):
Java Edition Alpha
v1.0.17 Slimes now spawn in multiplayer.
? Slime spawning has now been reduced as they now appear in abundance.
A miscalculation in the new limit has now caused slimes to spawn only in strange locations, so natural slime spawning has now been disabled.
Java Edition Beta
1.2_01 Slimes have now been returned to the game.