Does GHS weld teeth back onto carbide saw blades?

No.  A company called 'North American' used to do so in Conroe 20+ years ago, but they retreated back to the Dallas area at that time.

I think that they are still around up there but have no other information on them.

They were very good at what they did as they built carbide saw blades but they were the last business that did such work in our area as far as we knew then or even now for that matter.

Let us know if you know of someone in the H-Town area who does so.