Given the complete lack of correct hygiene practices that can be observed of the vast majority of those wearing masks, I'd suggest the chances are that this is probably 'safer' than a masked server.
This all depends on how much contact transmission is going on, but yes, it's possible a masked waiter (I don't personally like the term "server", it's a bit of an Americanism and suggests a bit much deference to me, not to mention that it's also a term for a piece of IT equipment) would be more likely to have some nice COVID on their hands (and so on your plate) than an unmasked one.
However, really, nobody in a restaurant should be leaning over customers at present, mask or no, they should be modifying their practices to avoid that, e.g. asking people to pass used plates over. Not least because, regardless of the staff, the customers pretty certainly won't be masked at the table.