Is the MIDIMATE II / MIDIMATE eX driver multiclient capable?

Not initially, if you use MIDIMATE II or MIDIMATE eX under Windows with the default driver (i.e. no separate driver installation). However, if you install our universal ESI MIDI Port driver, the device becomes multiclient capable.

Yes, if you use Mac OS X. This is a standard feature under Mac OS X.

A multiclient capable driver allows you to have multiple applications access the MIDI device at the same time.