It's an issue, but can easily be rectified. Both my DJ mixer (Denon X500) and Karaoke mixer (A&H ZED12FX) have record outs, or I can use the booth out on the Denon and aux sends on the A&H.It may well be the cleanest but what about levels? Were I a videographer, no way in the world would I depend on a DJ, who is not responsible for video stuff, to be responsible for putting a good level to my recording device.
I agree it's not fair to assume you will provide it, but I figure if I didn't, I would be the one either blamed or pointed to when a guest says "Why does he have 2 mics on him?", so it's really in my or your interest to make it work .. just get something in return.