There are plenty of reports of people vaping hexen across the internet (see reddit, for example). It's suppose to work extremely well. Very fiendish like a lot of other popular RC cathinones that have come before it.
I haven't tried hexen myself, but it seems indirect heat is the best way to vaporize it. Most people use foil, oil burners (aka glass dick), hallowed out lightbulb bulbs, etc.
I don't think putting a direct flame to it would work so well (it doesn't in the case of most cathinones) so I don't think a rose stem would work so well unless you kept the tip of the flame far enough away. You want to try melting the hexen into a puddle and then slowly continue to heat it until it vaporizes. Try it off foil or out of a glass dick instead maybe?