Is there a way to hide certain apps from the cmd+tab menu?
Yes, it is possible, however the only way I know of doing it also hides the dock icon.


  you must modify the file named 'Info.plist' inside the Application's package (i.e. Sherlock.app/Contents/Info.plist). Open this file in your favorite text editor and add the following section (if it's already present simply change the 0 to a 1 in the string tag):


&lt;key&gt;LSUIElement&lt;/key&gt;
&lt;string&gt;1&lt;/string&gt;


Source: Hide any program’s Dock icon - Macworld Mac OS X Hints

In the newest version of macOS, a string should not be set for LSUIElement. Instead, you need to use a boolean as follows:

&lt;key&gt;LSUIElement&lt;/key&gt;
&lt;true/&gt;


Before OS X 10.8, use this instead (note NS instead of LS):

&lt;key&gt;NSUIElement&lt;/key&gt;
&lt;string&gt;1&lt;/string&gt;