Collector currently can only take photos using the standard camera view. However, you can also choose to attach photos from the photo library on the iPhone/iPad. That allows you to attach photos taken by another app.
If you take a photo with your favorite camera app, save that photo in the Camera Roll on the device (or some other folder in the photo library). Then switch back to Collector and add that photo from the photo library. It would be nice if you could do this without switching apps, but that is not currently possible.
I just read about an interesting new app that could be very useful for doing exactly this, called Nav Camera. It overlays information onto the photos you take, adding location, date/time, custom notes, etc. I haven't used the app, but it looks worth checking into.