The 'comments' section on the NHS website might be of interest to you, as people who've had (or stil have) a frozen shoulder have reported on what has, or hasn't, worked for them. (Only one specifically mentions hydrodilation but the alternatives mentioned by others might also be worth thinking about):
http://www.nhs.uk/conditions/Frozen-shoulder/pages/introduction.aspx
I have no personal experiences with this, I don't know anyone who has been treated in this way, but one thing that comes to mind after reading the technique.........bloody painful.
The treatment I had from a physio was very painful (having my arm pushed back further than I thought possible until tears were in my eyes, but worked eventually.
Trouble is a few months later I tried to swat a fly and it jarred my shoulder again!
The physio has mentioned a few times that this is the treatment these days. I`m not too bothered about the pain. I nearly fell down an escalator a few weeks ago and instictively reached back to grab my suitcase which was going down with me and I wrenched the bad shoulder. It hurt so much that I was shaking afterwards. It can`t be worse than that. Anyway, I think they might use local anaesthetic.