I don't because I put my U-lock there. But basically, if you've got a pocket where the camera can be secure from jostling and won't be crushed, there's nothing wrong with it. If you don't or you're not sure, a form-fitting camera pouch from your local stripmall camera store will provide about as much protection as you need. If you need a camera bag that will protect your camera if you fall on it, start at Pelican's plastic cases; nothing less will be strong enough.

When I'm riding with a compact camera, I put it a form-fitting bag (about 1" larger than the camera on two sides) with pockets for data cards and batteries and stuff that in my courier bag, but that mostly helps with keeping things together; I can hang the smaller bag from one shoulder and reach the camera without rummaging around. When I'm traveling with a SLR, I either use its dedicated equipment bag or carry it in the courier bag, unpadded, VERY carefully, because it's not rectangular and so there's no simple safe way for it to be carried.