Whirlygig, technically, you can use any helicopter you want for IFR 'training' as long as you don't fly outside of it's certification. ie in actual IMC.
Can't think of any reason why not. I know one guy used to practice holds and ndb approaches in his R44, after he had a quite comprehensive instrument kit fitted.
You can learn all of the procedures in an R22/R44 if you want, as long as they have enough instruments fitted to allow it. There are a couple of IFR trainers of that type about. Some schools used to use the R22 for the IR course. They wouldn't be going IMC though.
Don't know of any other single eng helicopters in the UK certified for IFR/IMC training except for the Bristows machine.