I've been on on a gluten free diet for some time now and I just thought I'd offer up my knowledge where it might be relevant here.
Firstly rye products of any kind are definitely gluten (as are spelt, which is another common misconception (although in small doses that may be safe for some people)); I am not sure if the above above post had some confusion but, gluten is not a rising element, when stretched it creates elasticity in baked goods. Gluten free rising agents include bicarbonate soda, when pure and gluten free yeast (regular yeast for use with wheat flour may or may not be safe).
I am not sure about fermenting gums, but in normal gluten free cooking they are employed to crudely simulate the effect of gluten as they will absorb moister to swell up and add body/texture, which may make a person feel fuller. At the below link you can find information saying that texture may be more like real bread if you use substitutes such as flax seed rather than gums.
[url]http://glutenfreegirl.com/gluten-free-p ... tio-rally/
I have heard that it can be vary difficult to keep a gluten free sour dough starter alive for more than a week and many people recommend boosting it with kirfi (spelling) water so it reaches the desired level of activity before it rots. I will check out the above blog too after this post.
One thing thing I would say, although I can't find the blog at present, is that it has been explained to me that for celiacs even if there are no unpleasant symptoms gluten may still be silently damaging the intestinal wall in a way that will eventually lead to heath problems from food leaking into the blood stream. If you are just avoiding gluten as part of some diet then this shouldn't be a problem and including rye in your diet should be a personal choice.