Firstly, you are right that a NMC means that a player cannot be sent to the minors or waived without his permission.
But I completely disagree with the premise of the remainder of your post. Just getting a bunch of draft picks does not speed up a rebuild. In fact, the opposite is true. You have to go back to 2003 to find more than one or two players per draft picked after the top five that are impact players right now. It is likley five years plus before anyone in this draft picked outside of the top five could make anywhere near the contribution of a guy like Visnovsky. Assuming Penner is for real, and I sure hope he is, a similar statement could be made about him.
If the Oilers could get a second pick in the top three I would be more on board. Even the top five might interest me. But to trade away players that are playing too or outplaying their deals for draft choices is much more likely to perpetuate the team's current situation than it is to speed up the rebuild. Why not keep most of what is working. Perhaps deal a guy like Souray who may well have one foot out the door, make a strategic move here or there, but concentrate most of your effort on shedding individuals who are not earning their keep.
When I say speed up the rebuild, I don't mean we'd be drafting players that would instantly have an impact (outside the big three in this draft) that would suddenly make as a playoff team again. But the general thought is that the Oilers will need to continue sucking and draft in the top 10 a couple more years to actually turn this ship around.
My thinking is, instead of "planning to suck" or whatever you want to term it, Tambo should try to squeeze two or three season's worth of Top 60 picks into one. Visnovsky and Souray are not exactly young, and it's highly questionable whether or not they will still be impact players in three or four years when this team needs them to be. Unless Tambo truly believes that this team will be a playoff team with a healthy roster next year and some of the deadweight dropped (Moreau, Staios, Pisani, O'Sullivan), there is no reason to hang onto veterans, regardless of how well they're playing, if other teams will offer up high draft picks for them.
Penner is a different situation. I would certainly not trade him for anything short of a lottery pick (basically Boston's Leaf pick or Carolina). He hopefully will be a key cog over the next few years, as you suggest. But the two veteran d-men...there's that buy low/sell high saying, and they certainly won't become more valuable as time goes on. Visnovsky is a $6 million player, it's not like he's some great bargain that some people are making him out to be.
Should Souray and Vis get moved for assets, there will be players and free agents out there available to upgrade the roster with to hopefully make us a competitive team for the next couple seasons. There are those who are already planning next years tank, and I simply can't agree with that mindset. The goal of all 30 teams in October is to make the playoffs, and I'd expect Tambo's off-season moves to have that goal in mind. If things go bad again like they have this year, then might as well tank, but that can't be the goal out of training camp.