Yes, there exist people that got carried through the fight or otherwise have the clear yet cannot perform. The converse is also true: there will be those that can execute every mechanic perfectly while doing their job well, yet for some reason or another don't have the clear.

But these are the exceptions, not the rule.

Adding an option as suggested in the OP would improve the chances of making that rarest of things: a PF farm group that is actually able to farm. I agree it wouldn't be bulletproof, but it would prevent a great deal of grief and wipes/disbands.

To add to the suggestion, it should of course only be selectable if everyone in the party at the time of the PF creation has the clear.