If SERIN/SEROUT without flow control works across the BT-link (which it apparently is) then HSEROUT/HSERIN will work too.
My understanding is that serin never worked but serout did, post #44, which is why I suspect flow control, we were given the wrong impression when we were told using hardware usart had solved the problem. Do we need more information? or will this lead to more misinformation depending on how I read it.