Welcome!
Totally allowed.
It's an early UI animation of the Chief, similar to how he appears in the final game, but it's a hologram of him and it's pre-rendered. Seems it dropped down from the upper left corner, going by early screenshots. Here's the tool we have for working with the format:
Much of this was cleared up by Karl, one of the game's programmers, in this thread - this post explains the plans they had for the multiple raider types, and there's discussion of some unused/revised buildings throughout the thread, would recommend taking a read through the whole thing, it's pretty cool:
I heard the game has some old test levels (one per biome?), but their formats are outdated and can't be loaded. Don't know any details myself, would be cool to see them though.
Edit - Yeah, they're at Data\Levels\TestLevels. Dunno if anybody has ever tried figuring out what they look like, or adapting/remaking them in the final level formats.
Edit again - @Slimy Slug says the test levels can be made to work with some tweaks to the cfg, might be uploading a video of 'em.