Almost, but not quite. The M11/9 mags will fit a MAC 10/9 magwell, and they can be made to work in the Fat MAC. However, yours is not going to work with your current setup.
SWD designed they zytel M11/9 mags, and also changed the MAC 10/9s they finished with a different magwell and bolt to work with their mags. The mag catch is in a different location for the M11/9 vs. MAC 10/9. You will see the zytel mags have two catches so they can work with either gun. I had also been able to put a second catch at the bottom of the skirt on some PAM-2 mags. Here I was able to run these mags in both the MAC 10/9 and M11/9.
Unfortunately, the Zmags are only made with one catch. While Zmags will fit and latch into your MAC10, the mag will sit too low and the bolt won’t strip the round off the top. You could always buy some zytel or PAM-2 mags to run in your Fat MAC.
The other issue is your bolt. If your gun runs on Walther mags, it has a double-feed bolt, which is too wide for the single-feed zytel / PAM-2 mags. It would hit the rear of the mag.
Now you can get a single-feed bolt and some single-feed mags and convert the gun. Or you could buy more Walther mags. But your Zmags won’t work. Sorry.