Getting it straight...
Here's a concrete answer, and a solution. NO, there is no editor that is a for sure editor for JO. You CAN use QRadiant and GTK Radiant in preparation for the SDK (Software Development Kit) to port your levels to it. You can also use UGG's JOMap utility (See JK2.net's home page, at top.) to port your Q3 bsp files over to JO's code. It's still kinda buggy, but works nicely. Just for kicks, tests, and some sabering, you can use JOMap, but I recommend waiting for the tools from Raven (If they ever release 'em...) for your more 'flashy' levels.