It would not be safe to remove AppArmor in the sense of the word. You would be disabling a security system designed to be in place for protecting you. So it would indeed make you less safe. What you want to know is: yes you can remove it without side-effects but lessen that system's security with it.

But the changes to apparmor are quite minimal, if you just want to move the MySQL DataDir to another partition. In addition I would recommend moving it to /srv/mysql and mount your partition either to /srv or to /srv/mysql for that reason (depending if you have other services on that box you want to put into /srv).

Reason behind is, that ubuntu states the /srv mountpoint/directory the place for your own (custom) service data to be deployed (srv stands for service. Should contain server specific services related data. For example, /srv/cvs contains CVS related data.)

The changes to apparmor are quite minimalistic:

vi /etc/apparmor.d/usr.sbin.mysqld and search for /var/lib/mysql and insert:

  /var/lib/mysql/ r,

  /var/lib/mysql/** rwk,

  # new location of datadir

  /srv/mysql/ r,

  /srv/mysql/** rwk,

That is enough to satisfy apparmor and you can leave it in place without needing to fiddle around with uninstalling it.

Hope that helps!