The crank is lubricated by the oil/gas mix. You shouldn't have oil "pouring" out the exhaust, but blue smoke and an oily residue is pretty normal.
I haven't switched mine to premix as it seems to be running fine, the auto-injection systems on these machines seems to be pretty bulletproof.
The Haynes manual I borrowed from our local library shows a test you can do to check if your oil pump is working correctly as well as a procedure for adjusting the oil pump cable.
1992 Polaris Trail Boss 250 4x2