At first glance this is a good idea, if it's a class I outbreak. But if you're in the middle of it, taking the time to search pockets could cost you the moments of extra preparation it will take you to fortify an area to survive the outbreak.
If it's a class III outbreak money will be completely worthless anyways. Furthermore, if you're in an infested area your highest probability of survival is to spend all your energies focused on survival, fortifying an area or evacuating to safety. Cash is unlikely to increase the odds of immediate survival, and while you're retrieving it from zombie pockets you're vulnerable to the crowd of zombies behind you that heard the gunshots, but are not yet within visual range. If the zombies were carrying something useful like ammo, that would be different. But why would someone who wasn't out of ammo become a zombie?
There are no moral or ethical concerns here, since zombies are no longer alive and certainly aren't going to be spending money. I'm dubious about the practicality of taking money. In all likelyhood even hundred dollar bills won't be worth their weight to carry as opposed to ammunition. Where are you going to spend all this money, eh? Still, I suppose looting/finding money would be a strong sign of optimism, might help your morale a bit. I suspect that zombies smell pungently of rotting flesh/BO, and that they don't loot the bodies in the movies because the characters find the odor too repulsive.