Hypaspist, weren't really light inf, they wore linothorax and a big shield, and as far as I can see were some high ranked soliders. and were actually pretty heavy or atleast medium infantry.
hetairoi (companion Cavalry) are already in the macedonian troop tree.
also, you said greek troop tree, but both units you suggested are Macedonian.
Guys, for the Gladiators for bandits, that is a no.
They fought in the arena, and not all gladiators are spartacus! and even he was cut down and his army was shown no mercy, and they wouldn't be bandits, (I geus) because they wanted to be free.... and live....
so as far as for gladiators, maybe in the arena.... but not as bandits.
bedouins, are more like tribes that live from fishing and hunting. and I do not see how that would be bandits.
My small list of ideas, you guys just give your Opinion.
Germanic Raiders (small to medium sized groups, near the broder with gaul and rome, weilding two handed axes, trowing axes and light armour.
Run away slaves (Much like looters in native wearing no armour, with knifes and rocks. large groups (30-60)
Ilyrian Pirates, (some what medium armoured men, with javelins and sicas/spears/axes walking along the Ilyrian coast, in groups of 20-50 men)
Gallic Raiders (gallic infantry not bound to a master, invading northen italy in large groups, 30-60 men)
Pictic Warband, (britton soldiers not bound to the local king, and roaming britton for small parties they can rob and kill, 5-30 men.)