Hi,
If SERIN/SEROUT without flow control works across the BT-link (which it apparently is) then HSEROUT/HSERIN will work too. It's just a matter of getting it setup correctly.
Having an oscilliscope or logic analyzer and probing the signals as it enters/exits the PIC would help. Doing so with the "working" version using SEROUT/SERIN and the with the HSEROUT/HSERIN comparing what you get would most likely reveal the issue.

/Henrik.