Wow. There was a lot of discussion while I slept! Let me address each scenario below:
1) Both mars and dcmatcheck are correct. If you draft the Cards OF, you can for example use '21 Hornsby at 2B, '46 Musial at 1B, and '78 Simmons at C. The caveat is you may only use them once.
2) If however, you also drafted Braves 2B you could use Hornsby again in a separate season at 2B.
3) Only the wildcard player can be used in all 5 seasons. In version 1.1 that is the advantage to the wildcard player. I am pondering more exclusivity going forward but for now the rights you own to the wildcard player are strictly to be able to use that player from the team you drafted him for all 5 seasons.