I'm sorry, but I don't see Porter or Bulluck being worth the 'risks' associated with them. Porter is, simply, over the hill - unless he's willing to come in very cheap and - here's the fun part - shut his mouth and do as he's told (never happen), the 4-5 sacks he might contribute aren't close to worth the headaches. Bulluck is an older guy coming off a nasty injury, and he's not been in a 3-4 system, so you're asking him to adjust as well - is he capable of doing so? Probably. Is he a good guy and would he be good in the locker room? Sure, but are we really lacking leadership on defense?
Merriman is the guy that might be worth the 'risk' - assuming he tracks like most, he'll be clear of the injury concerns and his "character" issues aren't wrecking locker rooms - he made some questionable decisions and it blew up on him in a very public way. Assuming he's willing to grow up (and they would have to determine that from talking to him), he could come in and provide real lift on the left side for a few years. Is he worth losing a draft pick? Maybe.
Merriman, I could see it, maybe - Porter and Bulluck seem like major reaches to me, given what's likely to be available at that position in the draft.