You are allowed to submit whatever you want. There are several galleries and sections, so feel free to submit your cool photos... The Photomanipulation section is wrong used: all the photomontages goes there plus, the "non achievable photos by traditional mediums". Should be a Photomontage section and a Photomanipulation one.
In each section you will find a gallery description. That will help you to choose the proper section and gallery. However, due some miscategorization, a bot or admin will relocate the miscategorized photos to a "neutral gallery" (usually scraps) and you will be notified 'bout that, so you will be able to relocate the photo in the proper section If this isn't enough, just ask again