I doubt you can sign someone to a DP contract but have it not count as a DP because you lend him out. But who knows really, because MLS. Of course the "haven't-I-seen-this-movie-before" possibilities are amusing:
Zlatan on loan to MCFC until New Year's Day 2017. What could go wrong?!?!. Well for starters he and Guardiola don't get along. But maybe they make amends, and Zlatan scores 15 goals by Christmas. Then it is announced that we were not allowed to sign him directly as we have 3 DPs, and there was only an agreement-in-principle to sign with us in January 2017, and he was really on a regular full-season contract at MCFC with a break clause. . . . .
Just make it happen and pass the popcorn.
I think you only have to worry about their net salary impact. So, if you sign Ibra to DP contract and lend him out for that half season, then you have to get the other side to pay his salary for that time, or at least all but $220K of it.