Wait, what?
If you're trying to sneak up on something then you need to be aware it is there, thus at least one of the characters has to be aware.
If two rouges are wandering around in the dark I would simply do two sets of opposed rolls, stealth vs perception. If Rouge A fails stealth against Rogue B he sees them and vice versa.
If neither do then neither do, and if they both do they both do.
Admittedly this is probably a house rule, haven't cracked open a book in a while but it seems a fair way of doing it to me.
And with that, I would never allow any PC to take 10 on a stealth check period. There are always consequences for failing. Yes, they may not be immediately lethal but if there were none at all I'd simply say "OK, you sneak around. where are you going?"
This, though it's not necessary in my game due to non-rules lawyer muchkins, would also prevent "OK, why can't I move really slowly and take 20" type arguments as well.
Again, personal interpretation and likely a house rule.