If you're talking about the 2 options you get to choose when you're uploading/updating your beatmap, then it doesn't really matter. WIP/Pending is essentially the same thing, it's just that Pending allows BNs to nominate your map, but on the surface, it's really just the same thing.
If you're talking about actual WIP maps that are not finished yet then, it's technically allowed, but just read what the modder's queue has to say before you post, since some might not like WIP maps. Or just state in your post that the map is still work in progress.