Can I be on bluetooth tethering + wifi, and select which traffic goes through each?
You need to use what is known as "policy-based routing". I.e. you route the network packets not based on the IP address of the destination, but on different criteria.

On macOS this is done using pf (see the man pages for pf.conf and pfctl).

In your case you need to create a policy rule that specifies that packets with destination port 22 will be routed over the tethering interface.