If you couldn't do it, there would be no hybrids :) Yes, it is possible. I have never done it, but from what I hear, Echeverias have a very poor germination rate, so you need a lot of seed.

Tehya, I've seen a lot of technical info on hybridizing Echies and Haworthia on the British Succulent and cactus society forums. Someone there posted daily details of his entire process and lots of advice. It was focused on haworthia but he had done some echies too. I'll see if I can find it again, and maybe you can look too...