Few things I'd like to point out .
Its to my Belief that the Mandalorians will not be satisfied with Driod kills.
They seek honor and glory with kills of equal to their own lives.
Driods are not living breathing creatures.
The Mandalorians will work extra hard to get to the Cowards Grievous and Ventress , just to get the filling of Glory they seek .
Explanation: My use of Coward is for those who run instead of standing their Ground .
As far as I can tell , no one in the StarWars Universe has ran from so many fights as Grievous and Ventress in the face of REAL Challenge .
This argument works against Mandalore in every way.
You're right, the Mandalorians would not be satsfied with droid kills. There's no glory in it. Which means they will lack motivation on the battle field and ultimately loose the thrill of battle and wonder: why are we fighting this war again? With battle being all about glory for the Mandalorians, the lack of living beings to kill will only hinder their spirits.
If the Mandalorians know that Grievous and Ventress are cowards, how would killing them bring a Mandalorian glory? Being a coward is a major sign of being weak in Mandalorian culture, and they won't have the motivation you say they will to kill a coward.
BUT, if they do have this motivation, then any battle Grievous and Ventress are not at will seem like a waste of time to Mandalorians, and they will loose the motivation of glory in battle.