There are no IFR certified R22's. To be IFR certified, you have to have back up gyro systems along with various other things. It is possible to get an instrument rating in an R22 but flying actual IMC in one would be a very foolhardy thing to do.
Also, for the USA there are no regs requiring any special instruments (fitted in aircraft) for night flight. Depending on location, it's not always necessary. Flying over a busy downtown area for eg. Get away from a built up area and it can quickly feel like IMC. At night for long trips out of area, I used to file IFR flight plans in an instrument equipped Schweizer 300C then cancel near home base so didn't have to do the approach.