i asked ET about this back in feb.
below email answer from ET about use of dual elevator servos and tailerons.

Hi Mongo,

Thanks for the email.

Dual Aileron support is currently implemented. It is possible to do the
same for Dual Elevators, but since the Guardian only has one Auxiliary
channel we have not implemented this feature. For now, a Y-Cable and
mechanical trimming would be needed for the second Elevator servo unless
there are enough people that would like to see Dual Elevators as an option
instead of Dual Ailerons.

“Tailerons” have not been tested with the Guardian but if elevon mixing can
be used, then it should work to connect the Guardian to them as though they
were elevons on a standard delta-wing plane.

Regards,
Eagle Tree Info
http://www.eagletreesystems.com
Ph: 360-544-8543
Fax: 425-484-4131