Mike,

I use my Weatronic DV4 module on a Graupner/SJ MC32 transmitter, wich also has a internal voltage of 3,6V.
But the external ppm socket will give you 5V! I'm sure the Jeti transmitters do the same thing, or else it would make the external ppm feature on Jeti pretty much useless. Just forward the question to Mr. JetiUSA to be sure.
The only warning i've read on a Graupner support forum is not to use FrSky modules on the external ppm, the FrSky module seems to need more than 5V to operate reliable.

Regards, Bart.