Well this would not print anything, for one FireServer does not trigger a ClientEvent, however technicalities aside the answer is no.
It is my best understanding that the default player argument is thoroughly encoded and protected - and even if theoretically possible, ROBLOX would be quick to squash any backdoor that allows this to take place seeing-as it fundamentally disrupts the entire purpose of FilteringEnabled’s existence in the first place.
It’d be outlandish to hold a firm belief that the possibility for a system exploit of this magnitude to exist is there, so I’d say don’t entirely count it out but don’t overly prepare for it’s presence either.
I also see @Med367367 making the statement of “never trust the client”, and I feel like that statement is drawn majorly out of proportion - while it is true that you shouldn’t have data/weapons/etc rely on information from the client, to disregard all trust in the client would cause for a major deconstruction of a games features.
To recap: the default player argument of OnServerEvent is not exploitable in this manner.