Bad motor mounts have NOTHING to do with tire wear or condition. That said, are you SURE that what you feel is a tire problem? Bad motor mounts can put so many nasty vibrations up into the car that you won't know whether you're scratching your watch or winding your butt until your watch quits working.

Treat these as two separate issues. If the motor mounts are bad the replace them and go from there. They need replacing anyway.

If you know for sure that you have a tire problem then also correct that.

You can't expect to fix one problem and correct the other.