Can I use 1 Block Erupter 336Mh / s + 1 Block Erupter 1.6Gh / s. The mining rate is the sum of the two. Can I use the two together?
You can certainly do that. But you should take ROI into consideration when buying ASIC miners.
If he's mining with a block erupter it's obviosusly not for ROI reason.
I support mining to help the network, everybody should do it.