I hadn't seen Megaglest when I asked this so was very happy to see the Indians there. I've since added the woodsmen and romans to that and also have all 5 vbros packs, which I've gone ahead and added the Indians to with no problem. Sometimes I try to move something and the game crashes in the loading so it's trial and error but Indians work in all 5 vbros packs with no problem.
I have included most of the Vbros' factions, to name all of my factions:
Africa, Aztec, Ballz, Barbarians, Bugs, Canadians, Colonies, Crusaders, Dark_magic, Dwarfs, Egypt, Elementals, Elves, Goths, Indian, Magic, Mario, Martians, Moon, Norsemen, PC, Penguins, Persians, Pirates, Romans2, Science, Tech, Western, Woodsmen.
The only thing I found important: All data, which is included in a particular package file (for example megapack.xml for the Megapack), which are armor type, attack type and the damage multipliers, have to be included into the corresponding file of your collection and... to avoid the 'non-harvesting' bug (which, BTW, more likely seems to be a side effect): Delete the (as far as I know) not needed resources life, mushrooms and puff in the resources directory (these are included into Vbros pk. 2) - my Mega Glest (3.3.4) runs perfectly with this modifications on a WinXP SP3.