You can yes, but what breed? i have two flocks of calls... the parents & the kids, and then more kids lol So i definitely no longer have pairs in one pen, it works.. that said calls are VERY small and personally i am not a fan of mixing them with larger duck breeds. They can be seriously hurt.
When introducing any new birds, quarantine and i also suggest penning newbies within the existing so they can get to know one another without causing harm, generally as well, at least two bringing in single birds is a bit rough, not impossible not like chickens...but still nicer if the newbies have company till the flock sorts itself out.
some of my chickens and ducks co-mingle BUT no one lives together, ducks as said, messy, wet, muddy and chickens like dry... and dirt... also chickens fight mean, those pecks can take an eye out.
My calls are full flight but i have them covered and penned, i know some do have them loose and full flight too.. it's tricky and totally depends on your pred factor and ability for the ducks to remain around. I keep my scovies full flight but i free range and feel that is unfair to clip.
Call drakes are drakes they will try to mate any female they can, regardless of her size.. they actually have quite the moxie given their size.