Yeah, Xizor is free to hyperspace jump outta Coruscant. But he has to go 'somewhere' tangible. Just name a planet and its fine (how about that stronghold we saw in TCW?)
And that brings up a previous point Beni made. The combatants can't just go anywhere. (Unless Beni wants to clear that up a bit more)
Mandalore was quite skilled in battle, but obviously Ulic will destroy Guri.
Edit: and the Empress Teta system is like right next to Coruscant. So they will get there awful fast.