Yeah, I know about that statement. However, that still doesn't mean that Ultimax is actually region free.
Considering that the decision to lock Arena 1 was most likely the result of releasing the game simultaneously in two separate markets at highly differing price points with the same content, I would that assume that one of the following scenarios happens if they don't region lock Ultimax:
1) There is larger gap between the Japanese and the NA release.
2) The Japanese and the NA versions will have different content (read: only one language option), but get released almost simultaneously.
Personally, I'd prefer option #2.