I have a mixed flock - Pekin Ducks and mutt chickens (see Signature, below). Plenty of males. Some squabbling for feed, yes. No issues with attempted matings. I'm not saying it never happens, I've seen a drake chase a chicken (hen), but I couldn't say it had mating in mind, and the other chickens chased it off anyways.
Keeping your waterers clean is the biggest concern. Ducks will spoil a waterer with dirt, mud, bits of food, whatever VERY quickly. I avoid that by having multiple waters, some of which (including a "battery box" with a float valve for controlling the water level) get dumped daily. As well as most of a dozen "chicken cups". and a kiddie pool filled by rainwater. The duck can't use the cups well, but they love the battery box for dipping their bills and cleaning their nostrils. Since all the "stuff" settles to the bottom pretty quick, the chickens continue to drink off the top.
and of course, there are a few diseases that can pass between the species, but good biosecurity - which you need regardless - helps minimize that risk.