My horses have always nibbled on my roses with no ill effects, and I find absolutely no reference to roses being toxic on any of the umpteen zillion toxic plant lists that I have.
Same with grapes, and Mingus single-handedly ate an ancient grape vine that I had -- one that I had transplanted from a thoroughbred farm!
I found honeysuckle on one list, but that particular list included a number of plants listed as safe on others... Japanese honeysuckle is horribly invasive.
When Kudzu was first imported from Japan, it was widely planted as an alternative forage for cattle and horses a s well as for its large, beautiful leaves...however, as it has run rampant in many areas, you might get run out of town if you intentionally plant it! IIt can easily cover your entire barn, and perhaps a few slow-moving horses!)
BTW, while sunflower seeds are good for horses, the plants themselves are considered at least mildly toxic.