It's interesting that you bring up this question, as I discussed it elsewhere recently.
I've made 2 vindaloos recently using C2G's recipe and I ordered a vindaloo from restaurant where I can sense the use of vinegar, although mild enough that it's strong flavour notes are not highly noticeable. My take is that any acid that you would use to tenderize meat is likely to do a great work. I'm sure this is one of those areas where it's pointless discussing which is correct, mainly because a number of chefs will do it differently, CH's example is quite evident of it. I have bought a bottle of vinegar and I intend to try it in my next vindaloo/phal, if I feel the smell/taste of vinegar too strong, I'll probably not look paste the lime/lemon for this dish again.
Some other alternatives might be: pure citric acid, jif (watered down lemon juice/citric acid), tamarind sauce.