Essentially the issues are similar to fighting out of state with commssion bans.
One, most other regulated states won't let you fight if you are banned in any other state.
Two, if you do fight out of state while suspended elsewhere you will receive a lifetime ban in that states jurisdiction. Meaning if you are suspended with the NSAC and fight in Japan during your suspension the NSAC will no longer licence you or dramatically extend the suspension.
Three, since the UFC does not want to get in trouble with state athletic commissions again; they will not schedule a bout with a suspended fighter even out of the state of the suspension. For a UFC contracted fighter to try to take a fight outside the org while under contract would likely result in a lawsuit/injunction against the fighter stopping the fight before it happens. See Couture/Fedor.