Thanks Erland. We too have not had much luck on locating information regarding these accounts (except for how to recreate them). As you suggest, the fact that these come disabled is probably the greatest clue as to their expected behavior.

Since time is running out before go-live, we decided to just give it a try and thus far the instance and databases seem to be operating as before. PBM seems to be unaffected as well, so we are cautiously optimistic that we won't run into problems down the road. The passwords were just past their expiration dates when we enabled the CHECK_EXPIRATION option so we conveniently had some immediate results.

Hopefully this information is helpful to anyone else encountering this situation. If anybody knows of or learns of a situation where enabling the CHECK_EXPIRATION option is detrimental, I'd be very interested in hearing about it.