A couple thoughts,
First check that the chain adjusters are even
Second, use a straight edge. Or a longish angle steel or aluminum straight piece. Check to see if the rear sprocket aligns with the front sprocket. If they are lined up, the spacers should be correct.
It looks from the photo that the tire may be wider than stock. If so, the wheel may have been redished to pull the tire to the right for chain clearance. It is hard to tell from the photos.
You can do a rough check for frame straightness by running a string around the headtube and to the back off the bike at several places. Like one long piece from one rear shock mount around the headtube to the other shock mount. Then measure at different points from the frame centerline to see if it is symetrical. Do this from the swingarm also.
That should give you a good start.