Red-Dead-Redemption: Is there anyway to "win" the side "trap" missions?

I think you might be over-thinking this a bit. When I come across these missions I just go into Dead Eye mode and fight. Generally with Dead Eye enabled the fight is over pretty quickly with me as the victor.

The reward from them is the same as any of the random missions... increase in Fame and an increase in Honor. If you don't want or need either, then continue avoiding them.

Actually I've handled these fairly easy, the way I see it you've got only a few choices:

a) Stop and get there walking, leaving your horse at a considerable distance. Obviously prepare yourself for a couple of well placed shots in the legs (Not killing the robber) or get your rope ready if you like the challenge.

b) Shoot them on sight.

c) Get close with your horse fast enough for them to try and get you down but not enough for them to succeed, then run a bit more and shoot them or tie them with the rope.

The way I see it, you've got no choice but to fight, this is what the game is about and all missions award something, even the ammo (if any) is something you can't refuse, and you can even avoid using ammo by using your rope.

I like to skirt around to the rear of their positions, so that they are no longer hidden, then shoot them from behind. Except for the woman who baited me. Her, I hogtie and leave on the train tracks. Squish.