Nope, the /mu-plugins/ is for "all" blogs and anything in that folder is automatically installed and unless you (site owner) removes it from that directory, it will be auto-installed.
The /plugins/ directory is the only one where the plugin "shows up" in the plugins tab.
For instance, if you put a plugin like "change Blog URL" in the /mu-plugins/ folder, it will not show up in the Plugins tab since it is already "auto installed" and will show up to configure it in the Options tab.
Anything you put in the /mu-plugins/ folder is automatically activated and installed on every single blog.
Anything you put in the /plugins/ directory shows up on "all" blogs as well, but needs to be activated on a case by case basis in the Plugins tab.
Trent