Can I plug the receiver of my Sennheiser G2 into the microphone input of the Sony MC50u without damaging it? The input on the camera supplies plug-in power that I don't think can be turned off.
If so, do I need a special cable, or can I use a standard stereo mini phone cable.

I don't think the low voltage bias current would damage the receiver, though it may add noise, if it does, a blocking capacitor would need to be soldered in.
A standard 3.5mm TRS>TRS (stereo) cable will not work. As I recall, the plug's ring terminal needs to be floated at the receiver end.
The mini-plug to mini-plug cable that comes with the G2/3 EK100 receiver will feed both L+R channels of the recording device.. use that, or build a custom cable.

Thanks Rick, I'll have to search and see if I still have that cable. I guess it was probably a locking type.

I asked a representative at a trade show, and he called back to the factory. He claimed that the Sennheiser receivers are internally DC blocked up to the full 48V phantom power without damage to the receiver. I told him that it would be a great thing to have that in writing. Perhaps something that should be stated explicitly in the manual. Considering the 2nd hand provenance, I'm not sure I have 100% confidence. I would still like to see an official statement.

I have inadvertently had Phantom Power engaged with a G2/3, no damage was done to the EK100 portable receiver or the (SD302) mixer, though it did drain the the mixer's internal AA batteries rather quickly. FWIW, the EK100's output is unbalanced.