So in SS/2, DN mentions that any pot you play in, you should raise. That is, any hand you feel is worth playing is worth playing for a raise, and everything else should be folded.

Does this mean you should raise AND reraise with everything you're playing with, or that you can call a raise? For example, I have 237xx, and the UTG raises. Do I call, since I want to play, or raise, because I should raise anything I play?

Does the answer change if it's 2468x, since that's more marginal?

He means raise and reraise everything (I think). The hands that you mentioned (237xx and 2468x) are excellent, and should be reraised like crazy. Most of the time, the UTG raise means he has 2 + two other wheel cards, or a 1 card draw to a non-straight 8. You aren't worried about these hands because they aren't really any better than your hand. But you have a common interest in driving out everybody else! You are capped at 4 raises anyhow (preventing you from getting wiped out from an unlikely made 7 or 8-5), and you should be happy to get all your money in early with these hands. Let's look at the hands individually:

237xx - This is a solid hand because you are drawing so smooth. If you make your hand you will probably win. You essentially have two draws to improve, because with the huge pot you build before the first draw, you will always call a small bet after the draw because of great pot odds. So your opponent won't be able to intimidate you out of a real chance to win the pot. If you don't raise, you get more players but not necessarily a bigger pot, and there is a chance of a raising war after the first draw that might prove expensive if you are still drawing 2. Who wants that?!?

2468x - It's true that the best you can do with this hand is 8-6. But 8-6 isn't so bad, it is just vulnerable to people drawing out on you. So you have to eliminate people before they get hands. Raise and reraise!

246xx isn't as good because of the diminished possibility of making a 7. In this case, you are planning to get out if you draw 2 blanks on the first draw, so don't commit yourself to the hand by reraising. It is still good enough to play for 2 bets though, and any opening raise will send the BB and SB packing if they don't have a 2.