I've done cannabis>cannabis grafting on an outdoor plant, it was unknown bagseed onto a LSD. I've always liked the 6 strains on one plant idea,so when i found a branch broken off a plant ,i cut it back to a wedge shape,cut the notch of another plant where a branch came off the main stem, stuck it in there, tied it up with sewing thread,wrapped it in a moist paper towel, then wrapped it in cellophane, worked great, just had to keep the paper towel moist, and i changed it every couple of days to keep mold and bacteria down. Because of the unknown strain it never fully flowered by the time the base plant(LSD) was ready to harvest, and with the weather turning i didnt bother leaving it with the one branch to finish.
As far as cannabis>other grafting,its definitely an interesting idea, and probably loads of fun to play wiith, I know Ive devolped a want to play with horticulture, but other than for fun there's no reason to do it..
Re vegging an establshed cannabis root stock,adding cuttings/grafts, then flowering seems to be another beneficial aspect of grafting,although i havent tried it and am not set up to try it...
either way this shit really interests me