Plainsman,
I don't personally load either of these cartridges with BP. However, I can see no reason not to. I have been tempted to load some .44 magnums just for the fun of it.
The 444 Marlin should make an excellent BP cartridge as long as you apply BP loading techniques to it. It's case shape is very similar to a number of historic BP cartridges. It would not be a legal cartridge for silhouette.
Go for it.
Y'all be good.
horsefly