The 96 ECU is one of a kind unless you have the ability to flash them, in which case most 96 or later jeep ECUs should reflash to be a 96 one just fine iirc.
As for the evap purge solenoid - it's covered in section 8W-30 of my 96 FSM, page 10. Wiring is:
* circuit A0 (red) from battery positive terminal -> fuse 8 in PDC (60A) -> circuit A1 (red) -> ignition switch input -> ignition switch start/run terminal -> circuit A21 (dark blue) -> fuse 18 in PDC (15A) -> circuit F12 (dark blue / white) -> evap/purge solenoid -> circuit K52 (pink / black) -> ECU cavity C20 in connector C165.
So yes, it's powered via a wire from a fuse and turned on via a ground-switch line from the ECU. This is generally how most automotive stuff is done, as ground-switch circuitry is cheaper, simpler, and more durable (n-channel MOSFETs vs p-channel, and ground referenced gate control vs charge-pump circuitry being required.) In fact the only example I can think of on the XJ that's positive switched directly by a computerized device is the AW4 shifter solenoids, all 3 of them are positive side switched. Most other positive side switched items in the XJ are relay controlled, with the relay coils being negative side switched by the ECU.