The thing you have to remember, drafting Hochenson or Sternberger or whoever at TE isn't going to be deterred due to having Graham, Lewis or Tonyan under contract. A rookie TE, no matter who it is, isn't going to break the bank nor is he going to be expected to step right in and be a game changer. Any TE the Packers draft is an investment in the future. Also, Tonyan isn't a lock to make the team, none of his money is guaranteed. Not to mention that the Packers may carry 4 TE's. All that said, I think the Packers pick a TE pretty high, who that ends up being is anybody's guess.
One other note, saying "you can't spend high draft resources on a player, because you already have too much invested (Graham) in the position", is poor planning in my opinion. Graham so far hasn't lived up to expectations and probably at best, has 2 seasons, more likely one, left in GB.