Hi Diki
You can never be 100% guaranteed (Even hardware can’t achieve that) but apart from those uses that have modified the OAS system files, I am not aware of anyone having any problems occurring in normal use.
The polyphony for the VSTs is variable (Depends on computer specs) and the way the OAS system works (Although you will need to ask the engineers if you want the technical specs) is that if you exceed the limit, the least significant note drops out. (This drop out does not affect the OAS voices (Which includes Akai samples) as these are processed separately by the SG12 PCI card)
You will need to contact Wersi Germany or Helmut Eder of Wersi Austria for more technical details.
Hope this helps

Bill