Paul Remde wrote:

is wondering if he can mount a TE probe on the fin and connect it to the
variometer, or will the propwash cause problems.

The vario will not be too accurate in the propwash, but who needs an
accurate vario when the prop is turning?

Is it necessary to use
some sort of pneumatic switch to switch between TE and static input for the
variometer?

Not necessary, but recommended.

Stefan