AFAIK, the 9x18 Ultra and 9x18 Police are the same. The 9x18 Makarov is a different round, larger in both case and bullet diameter than the 9x18 Ultra. The Makarov round will not chamber in a gun chambered for the 9x18 Ultra, and the latter is too small for the Makarov chamber though it will fit and fire.
Note that the 9x18 Ultra has a rebated rim, possibly so some tooling for the 9x17 (.380 ACP) could be used, since the rim diameter is the same. 9mm Makarov cases can be made from 9x19 (9mm Parabellum) cases by trimming, but some swaging would likely be needed to make 9mm Ultra cases from 9x19, plus the rim diameter has to be reduced.
As noted, one big difference is that 9x18 Makarov is readily available, while 9x18 Ultra is just about obsolete and is on the verge of collector status.
Jim