Hi there,
Sorry to hear of your frustrations. I'm not really sure what 'normal' treatment is- it does vary a lot depending on level of PT experience and even country to country. But I will answer your questions from my point of view as a physio and give as much justification for this as I can.
So I think you are right in wanting to try glut max activation exercises. Basically there are two hip extensors- the glut max and hamstring muscle group. If one of them is defective, the other will work like crazy and be over active. So no amount of hamstring stretching will change the fact that it is overactive. If you learn to engage your gluts, it could actually give the hamstrings a break and a fighting chance to relax.
Muscle tightness is almost always a secondary problem- secondary to excess load, poor postures, pain, uneven muscle patterns etc and so generally speaking stretching shouldn't be the only line of treatment. Often muscles tighten in a protective pattern (which implicates neurological structures and involvement) to protect an injured joint or ligament and so needs to be a addressed at this level. Stretching a muscle while not addressing why it was protecting tensing is not likely to be helpful and may cause more problems.
There has been a lot of work done by Peter O'Sullivan and colleagues in research about best practice for SIJ dysfunction issues. Look for his papers if you can. Basically, with chronic SIJ problems, it is likely that there is abnormal muscle use around the pelvis which is a strong driver of the condition- this includes the abdominals (transversus, internal/external obliques, rectus abdominus), pelvic floor muscles, diaphragm, adductors, glut max, glut med, multifidus and lumbar erector spinae. So a good physio should assess these structures and give activation and postural control exercises around the pelvis. It is really important to consider how you are using all of these muscles and in what pattern you use them in day to day activities and sport. Stretching alone is unlikely to be helpful although it may be used as part of a solution for correcting tight strong muscles versus weak, long muscles.
Hope this makes sense.