I haven't done a Sony to an HVX, but I have tried to slave a Z1U to a DVX. I couldn't get them to talk to each other. I had both in Free Run, tried to slace Z1U to DVX and vice versa. I'd be interested in knowing of anyone has been successfull.
Both cameras have to be on speaking terms in order for jam sync to work, so you'll temporarily have to change the recording mode.
If the HVX is in a DVCPro50 or DVCProHD mode, it won't understand the timecode coming from a DV/DV25 or HDV camera. Put all cameras in DV mode, jam sync, and then switch the camera back to whatever mode you want to record in.
Also be aware that the timecode can drift when you switch into and out of MCR mode, so you should avoid doing that unnecessarily.
Beats me how the procedure works on the Sony, but you'll have to set both cameras to a compatible recording format first, so the HVX has to be set for standard-definition DV25.