I'm not buying any but as I am surfing the web I was wondering about these wheels and others just like them. I see a lot of different ones being run on buggies at WBB so...

Go-Cart wheels...They have a huge hole in the center of the rim, ranging anywhere between 1" and 2.5". Then it looks like an adaptor plate that would bolt to the rim which usually has a 5/8" bearing so....Here's my question.

Can you replace the 5/8" bearing and then use/find a bearing that would match my flexifoil buggy bolt pattern 12mm and run wheels like that?

You can, there is a set of wheels for go-kart's that we tried out, I think they were called tri-stars or spinnoffs or something like that. They came with a 5/8" bearing and we rigged them to fit a 20mm bearing in them. The two issues we came into was that the 20mm bearing was so small that it burned up within 10 minutes of riding, it was just not possible to get a decent sized 20mm bearing into the small center that these wheels had. The other issue was that because of the side loads that we were putting on the buggy, the centers of the wheels were cracking and blowing out...something you don't want to happen at 40mph.

Be careful on what you try out and make sure it can handle the loads before really putting it under stress.