Not really. You can have a mercenary that follows you around, and some characters (like the Necromancer) can summon lots of creatures to fight for you.
However, you can only directly control the one, main character.
You may want to see if there are any mods for WCIII. Some other people may have made ones very similar to the Orc campaign.
I would also check out Myth (1, 2, and 3), if you haven't seen it, yet. That's an RTS with RPG elements in the plot, but not so much the gameplay.
World of Warcraft (by Blizzard) should be coming out this year. You might like that.