Can the SPI pins of the BT800 be used as a main host interface?

Answer

No.  The purpose of SPI interface is to access the module inner settings such as selecting different WLAN CO-EXIST scheme, enabling HID proxy mode and so on. Furthermore, the SPI interface can be used to put the module in RF test mode. However, you may not use the module over the SPI interface for normal operation as main host interface.