I was wondering about hindering terrain. Does hindering terrain block the clear line of sight or does hindering terrain not affect it.

Example: My nightwing wants to outwit my friends bcf on his spiral, but the line from nightwing to spiral crosses a tree. Does nightwings outwit work or not?

please let me know.

Hindering terrain by itself does not block line of fire so Nightwing could outwit Spiral. If Nightwing was attempting to outwit someone with stealth then the stealth ability in combination with the hindering terrain block line of fire (preventing the outwit).

Also any line of fire that crosses hindering terrain grant the tartget +1 on their defense value. This is not cumulative, so if it crosses to squares of hindering terrain only +1 is awarded to the defender's DV.

But if Spiral has a Batman Team memeber on her team, then wouldnt she then be Stealth (by way of the MOD team ability) and nightwing couldnt outwit her?

That would be true if that were the case.