Well, I am a self admitted noob but I think most of them are not particularly useful, except in rare circumstances (like needing an arrow catcher, *any* arrow catcher).
There are definitely more than sages, though. I almost always use indie scouts in the early game since I can only produce one commander per turn in my fort. Longbows and xbows are useful for most nations. Some others I only use with a few limited nations (for example, with BF Ulm, I use the cav commanders that have better leadership than my nationals
).
Pretty much all standard indie infantry (I am not talking about special site indies like mages) is pretty useless, imo (possibly excepting the 10/10 LI with the javelins). Yes, if you find yourself without an arrow catcher or you want emergency PD recruiting, they are...well, I can't bring myself to actually say 'useful' but they are a lesser evil
Just one noob's opinion !
- Kel