Often is the short answer! It's a very useful feature. For example, I play Pennsylvania 6-5000 with the words being shouted by the band on the original Glenn Miller recording.
And remember that when making MIDI pads, the number of sounds, effects etc that you can use is limited. The easy workaround is to record the desired voice, effects, playing techniques etc as an audio song. That can, if required, be exported, normalised or processed in an app like Audacity and then loaded back in, whereupon you can link to the imported song file as an audio multi pad.
I've had students do this and I do the same on the Genos. I need a muted trumpet with pitch bends, growl and wah-wah for one piece. OK, pitch bend is easy and I can use a combination of cut-off, resonance and the mod wheel on an SA or SA2 trumpet for the wah-wah, but the growl will have to be done in the computer. As I don't want the reverb to growl, I'll record it on keyboard with no reverb and add it in Audacity.
As for looping audio files, with a bit of practice, this can also be done successfully in Audacity