are wildcards seeded?
if yes, can there be a reason that a WC is not seeded?
Wildcards are seeded only if their current ranking (week before the tournament) is high enough. Hewitt, receiver of many WCs lately, has never been seeded with one. If Djokovic should take a WC to Basel, however, he will be seeded #2. If he takes one to Valencia, he'll be seeded #1.
Pete Sampras once - as world #1 - asked for a WC to Vienna and was turned down, they had none left. He still got in as Boris Becker renounced the WC he had been given. So there is no absolute guarantee even for top players to get one. When he first was in, though, he was seeded #1.