I am one step behind you, having just bought the granite for our outdoor kitchen. I will be asking my fabricator this question now. We tore out an existing outdoor kitchen and granite. Now that I think about it some of the seams were just butted together and part of the seamed/glued on bullnose had fallen off, which would happen if the epoxy/glue broke down. I attributed the problems to poor construction and 10 yrs of use.

I bought 2 slabs to make sure my 12 ft section has no seams, but I don't want any seamed edge detail falling off in a few years!

your seams should be epoxied. I am a fabricator in MN and we do outside kitchens all the time. If the seam is done properly (at worst the thickness of a razor blade) no appreciable amount of the epoxy is exposed to UV rays in any case.

the only qualifier I would add is that you might alternately use silicon for the seams if the construction is such that a lot of settling is expected such as a deck. If it's built on a foundation like a house then epoxy is OK.