Organisms are host to their memes, and to the genes of their gut bacteria

Unless the gut bacteria where somehow only transmitted from say mother to children.

That is certainly not how most human gut bacteria work!

But where does this leave "driving genes" - alleles that help themselves rather than the bearer.

Yes, some animal genes can act like parasites. Most animal genes are not like that, though!

After all to consider regular usage the mitochondria - rest of cell relationship is often considered a symbiosis.

Yes, that is still reasonable - mitochondria have different genetic interests to the host cells - e.g. they want to kill males. If that was the context, the term "symbiosis" would be fine.

"Host" terminology is still quite stretch, IMO. Symbiosis takes place when different types of creature live together. Cloned somatic cells are better regarded as being part of the same organism. The genes are not really in a symbiotic relationship with the "host" - there is only one creature involved here.