never grown hemigraphis, looks interesting! i have used mucuna and various piper species but i dont find them good. mucuna is great as a green mulch you intend to cover a field, but even medium sized trees it will totally cover pretty easily. i think vines should be ruled out for said reason. also, although orchards may be different, in vegetable production with plastic mulch, piper style vines, like the sweet potato, will go all under the weed fabric and take up a lot of the fertilizer. i would use it in a tree closed canopy setting maybe, but not for row field culture, its not awesome in the sun either but will grow.
I think as a basic rule for ground covers to be used while intentional crops are in production, vines and things that send runners/rhizomes outward cannot be used. the extra amount of fertilizer used is cost prohibitive in many cases in my opinion.
the peanut seems interesting too, want to try that one out!