I'm not necessarily sure the centipede-like thing was an indicator of genetic mutations/splicing. It might have simply been an Alien which birthed from a non-human host. What's off-putting about it is the stylised nature of the art. If it was depicted in a less cartoonish fashion, I could see a design like that being rather nightmarish if on screen. I can't imagine it would have been authorised for just a cameo, mind you, considering how these things are usually budgeted.
The one with lots of heads might have arisen from mutation, but who knows?
I don't mind genetic splicing/mutation in a film the Aliens feature in. If any horror concept is suited for it, it's them and 'The Thing', after all. It just depends on how it's executed. The Ripley clones are actually fascinating to see when revealed and one of the more memorable scenes in that film with a fairly decent atmosphere. The one with the mouthful of sharp teeth and no eyes really intrigued me. Heck, AC's laboratory David 8's been busy in, seems like it's the highlight of the entire film for some people. I'm sure the recent 'David's Drawings' book was snapped up precisely because of that when it was published.
So, yeah, I don't have a problem with it as a basic concept. Depends how it's done. And if some of these are as a result of birthing from non-human ET wildlife hosts, I've actually wanted to see that done properly on film for a long time, so long as the designs look dangerous and believable.