I don't know if he would have offered them immortality of their own - I think he's too selfish to share the secrets of the horcruxes and the complete truth about them with anyone. But he did offer them power, which, as we all know, is very seductive in its own right. Power over the rest of the wizarding world, but not an equal share with him, though he was obviously very good at making many of them think they were 'special' to him.