It depends on the provider you go to, just like anything else there are excellent providers, and those that are so-so. Depending on the root cause (muscle length, tissue quality or joint motion/alignment) an ART certified chiropractor might be your best bet. activerelease.com has a provider lookup and it will list their credentials as well (DC, MD, PT, ATC, LMT, etc). The SI can refer pain all over the place in the low back, hip, leg, butt.
ART addresses soft tissue adhesion/scar tissue which is arguably the most common, and most overlooked musculoskeletal problem. It can happen in one of three ways, a big injury, a lot of little injuries (repetitive stress injuries, training imbalances) or lack of oxygen (sitting for extended periods of time).
Adhesion can glue the muscles together, stick nerves to muscles so they can't glide as they should, and decrease the ability for the muscle to produce peak torque. So before I get on too much of a tangent, yes it is focused on soft tissue quality, but if a muscle has adhesion, it won't be able to reach its normal length. Adhesion can also cause an alteration in joint alignment.