OOC: "It's perfectly okay to rule that..." does suggest it as being more of an optional extra.
But the Rules Of The Game: All About Movement article makes it more explicit:
http://www.wizards.com/default.asp?x=dnd/rg/20040622a
"Tumbling is part of movement, so a Tumble check is part of a move action. Any distance you spend tumbling counts against your movement for the turn. You tumble at half speed, as if each square you tumble through costs you 10 feet of movement (15 if you tumble on a diagonal)."
So the second interpretation above, that Tumbling is square-by-square rather than a full movement, would seem to be correct. Well, more correct. :) Both versions are legally correct, as they are from official sources. So, I'd rule in favour of Quinlan's tumble-move. (Yes, I've backflipped on my previous post. I'm a scientist, I change opinions in face of new evidence. :D)
Now, the Hide thing. This is two issues. To quote the Hide skill: "If people are observing you, even casually, you can’t hide. You can run around a corner or behind cover so that you’re out of sight and then hide, but the others then know at least where you went." This is exactly the case here: Quinlan moved and hid behind a pillar, which offers cover.
Of course, Renaldi still knows exactly where he is. (As an aside, hiding behind one pillar is pretty obvious. Using the cover of that pillar to move to a less-obvious hiding place is more effective.)
Now, the second part. "It’s practically impossible (–20 penalty) to hide while attacking, running or charging." The key word here seems to be 'while'.
The FAQ gives an example of a Spring Attack hide-attack-hide between cover/concealment routine which I'll use for an example, since I can't find a better one. Quoth the FAQ: "In this case, she’d be considered hidden when she made the attack, although she’d have a –20 penalty on her Hide check." and "This means that the character could begin hidden, move up to a target across open terrain, and make an attack while still being considered hidden (although she’d still suffer the –20 penalty on her Hide check)."
So, Quinlan is hiding. Quinlan is attacking. So he takes -20 on the previous Hide check. After all, Renaldi just watched him skip away, go around a pillar to face him again and shoot at him, and shouldn't be surprised in the least.
(Which makes a basic backstab from the shadows rather tricky, but I don't want to get into that now.)