I have the PMDG MD11 and it works just fine with the Addon Manager.
However, there might be a problem with it, because it installs the VC++ 2008 runtimes, and there was a known bug (Microsoft's fault...) that if you installed the VC++ 2008 runtimes on a system with the 2005 runtimes, the 2005 version would stop working, and that is the one that FSX itself uses, and we need for the Addon Manager too.
It's possible the problem doesn't happen if you have different releases/updates of the VC runtimes, which are usually installed with the various Windows updates.