Can i use cleaving finish to cleave into enemies i teleport to, or would this be only possible with a generous gm?
The feat says in reach, but with dimension door full attacks, everybody you can teleport to is basically in reach.
It reads like 3.5 cleave. The feat does not say as part of a cleave, or when cleaving, it just says whenever you reduce an opponent to 0 or less hp, you can cleave someone "within reach". It does say it will only grant one such extra attack a round, though.
Now, that having been said, "within reach" before you move would probably be the intent, but with dimensional dervish feats, you're moving as part of a full attack action...
I'd probably allow it.