The harness also has two connection loops, one on either side of the hip belt. Is there any reason I cant connect the harness to the tree rope on one of those loops instead of the back strap? Will it provide as much safty?
Those loops allow to hook the rope around the tree and use the harness like a lineman's climbing belt. It is really handy when trying to install strap on treesteps but I would not use it as an alternative to the actual way that they harness is supposed to be utilized.
If you find that particular climbing harness troublesome then take a gander at some of the new harnesses that Summit has out. The Fastback harness in particular is a breeze to put on because of its particular design. Well worth it in my opinion. If you choose not to go that route though then I would suggest following MrFritz44's recommendation and watch that instructional video/DVD intently.