I really admire you and everyone else who works in rescue with these poor dogs that have not been treated kindly. Your patience and perserverance are amazing.
I had 2 foster dogs that I bathed before they ever set foot in my house outside their crate. I think I was just very lucky as these dogs had obviously not had a bath in years, but they took it very well. And I had to cut HUGE mats out of them, too! They were very tolerant, thank goodness! I think my ignorance of the possibility that they would object turned out OK. I wasn't about to have those poor filthy, muddy, flea-bitten, matted, smelly dogs in my house without a bath! Maybe they could tell I wasn't going to have it any other way, so they thought, "Oh well, we'll let the crazy lady wash us." They were really good and of course I was as gentle with them as I could be, talking to them, cooing, etc the whole time. I think they were so starved for kind attention that they were only too happy to put up with the bathing to get it. I don't know what I would have done if they had put up a fight! It never occurred to me! In fact, now that I think about it, if I had really been worried about them objecting, my hesitance may have triggered them to get upset, too. So maybe it was all for the best.