Is 2xAMD GPU on SLI motherboard able to work?

Below are using oclHashcat-plus.

1) Having a SLI motherboard, just wondering whether 2x AMD HD5870 able to work at the same time?

2) Without activating crossfire mode, I simply plug in 1x 4850 and 1x 5870, is this combination able to work?

3) To have oclHashcat-plus work properly in dual card, is SLI or Crossfire must activate or simply 2 identical card without SLI or Xfire still able to work?

Sorry if you find above questions are stupid but I just want to find out before invest money on system that turn out to be useless.

Thanks