Not sure what case you got, but i tried my Razr in the holster case (kind of vulcanized rubber to look like leather, with the kickstand) and it fit on the HDMI dock (Sales folks said the only diff between MultiMedia St and HDMI dock is that "Station" comes with the HDMI cable...no difference in the dock itslef? Then there's also a "Premium Docking Station" that has 3 USB ports; I might have that wrong and there's only 2, not 3 models?).
If the front of all these are the same, there's a clip on the front of HDMI dock that comes off. It is the plastic piece that would be in contact with back of phone when docked, covers the entire face of dock. You can see that the top of this piece will kind of pry off, makes it feel like its just a chincy build. If you keep pulling that, it will feel like the facing will snap/break, but it won't...i made the Vzn guy do it just to be sure. Just keep pulling and it will come off, giving you a bit more space for case with dock. It fit just fine for me in the store, even had a bit of gap with the case i had my Razr in.