Seam adhesive for vinyl is basically pvc glue...you can get some at a local carpet supply store or even a retail store for that matter. There is matte and glossy.
Each vinyl manufacturer makes an adhesive particularly for their floor - Mannington, Armstrong, etc. Best results will be achieved if you use the adhesive made especially for that vinyl. But most vinyl flooring adhesives will work OK on any vinyl floor. Do not use hot melt. It will not bond as tight and the gloss level will be different.
at this point knowing who manufactured the stuff is going to be a moot point.
we don't particularly use the manufacturers name brand adhesives. And don't have any complaints....it's all really the same stuff. We just buy matte and glossy. Don't matter what brand, and we've never had a claim on a vinyl seam that I know of. But we always use premium glue and the proper notch for our trowels to make sure it sticks in the first place.
not with sheet vinyl. the vinyl seam sealer glues the plastic together on the surface. you will always see a seam in sheet vinyl....it's just one of the characteristics of the floor. you can always put a top metal on it.....I see it quite frequently in homes since many do it themselves around here.
You heat weld heavy commercial vinyl like you see in hospitals. You can't have a place for any moisture to go because of health reasons. But it's pretty expensive and takes some skill.