Tricky. Definitely depends on the demeanor of the drake.
I have three flocks of calls, 2 are penned, one which was a trio till end of last week... free range with a HUGE flock of ducks, mainly muscovy, and some Pekin and buff and buff crosses. Plus chickens. So were talking more than a 100 birds here mainly huge compared to them.
They have been out there since i weaned them from my house, i raised them due to a dumb call mama saying stuff it lol. Often they kick about with the pekin and buff mixes... which include many drakes, since they do speak the same language, birds of a feather lol(scovies are not mallard derived, in case you didn't know).
That said i had one of my female calls which was penned fly out one day(they are full flight) and darn it all one my scovie females went for her! One time i would have said no way would i have calls around large ducks but i have changed my mine but will only say caution, caution... only you know your birds, only you know who is overly aggressive and only you are there to witness concerns.
Large birds CAN and DO kill those smaller than themselves, heck some small ones are so bold they will take on anybody too. Flock dynamics are very personal and complex, so always have a back up plan and watch very closely for intro's!