are stealth units targeted by flames from afar..?

[archaeolept]

yeah but this is no so serious issue since blood is better invested in vampires anyway

maybe in the late game when you are winning the dominion race anyways, i think. Devils seem better for crushing the heathen in the middle.
In theory, you could pump near twice as many, given hammers, as you could vampires; besides earlier. It is, however, more trouble to organize these devil factories.
A VL can easily summon more of his kith as well as his kin.

his would actually make good sense thematically - after all you have to be a Used Cars Salesman Of The Year to sell your soul to the Devil twice

well, thematically, their sure ain't only one Devil...
;-)