I really dislike func_get_args in general because it makes parameters invisible on the public API without explicit correcting documentation (and grabbing parameters out of thin air, which is what func_get_args() does, doesnt look very appealing in the code, too).
Combined with the fact that this would really be only a very small convenience, I have to say no on this one. Sorry, but thanks for the suggestion.
What would probably be acceptable is: EntityManager#persistAll(array $entities) but then we would need such a method for remove/merge/detach as well. Sounds like too many new methods for me that will be rather rarely used and we dont want to bloat the public API like that. And it really is a one-liner in userland code:
foreach ($entities as $entity) $em->persist($entity);