I too have had frozen shoulder (in both shoulders, not at same time).
Unlike the microvascular complications, there's no indication that high bg's are a risk factor for frozen shoulder. Biggest risk factor seems to be number of years with diabetes. There is some research that shows correlation between lower average bg's and frozen shoulder, but that may just be a byproduct of the fact that diabetics with very high average bg's don't always live for so long that they develop frozen shoulder.
Frozen shoulder happens in both T1's and T2's. It is more common in insulin dependent diabetics, but that might just be a byproduct of the early age that T1 often starts and the fact that number of years with diabetes is the biggest risk factor. It is less common in T2's on oral meds, but still not rare. Some of those "T2's on insulin" might actually be T1's that were not correctly categorized at diagnosis. One of the better recent studies, I think removes the "misdiagnosed as T2" effect in statistics by including the insulin dependent T2's with the T1's.
Some references on the statistics I cite above:
Note the last reference above, like many earlier references, finds that frozen shoulder is slightly more common in those with lower A1C's than with higher A1C's.
That anti-correlation with A1C's, combined with my suffering from frozen shoulder!, sparks my belief (no scientific paper to back me up) is that frozen shoulder is a kind of auto-immune inflammation which is not too different than the immune system attacks that destroy the pancreas in T1's or work against the efficacy of insulin in T2's.
Physical therapy eventually helped. My experience... there's certainly a sharp spiky pain in the inflammation stage. Eventually the inflammation dies down and physical therapy helps helps break up the scar tissue from the inflammation. The soreness that comes from physical therapy after the inflammation is gone, is a different kind of soreness (not so bad).
I had steroid shots into the joint and for me those steroid shots really marked the turning point towards getting better. Yes, the steroid shots also drove my bg's up and I had to compensate with more insulin. The orthopedist who did the steroid shots specifically chose a steroid mix and dose and administration that minimized effects on my bg's but those effects were still there. I strongly feel that the steroid shots were worth it, they reduced the inflammation and let the physical therapy break up the scar tissue in the joint.