haven't looked at the original Japanese manga in a while, so i had a look. he does actually say he can digest the cells of all living things and copy exceptional traits from their genetic information. That much is clear. I think we need to be cautious in our assumptions though. it's likely he could absorb the cells of the relic or ark, but we can't say for sure whether it would have traditional genetics. Let's say that it does have genetics that aptom can read, it still wouldn't give him any exceptional abilities, because all of the weapon systems of the guyver and gigantic are coded from the control metal and nav sphere. we have no idea what a relic ship lifeform would be capable of without a nav sphere, maybe it only has basic metabolism functions, and a potential to accept programming and adapt it's form and function based on input data. but then, since that is something the creators seem to do habitually, I don't think that's special. human cells accept data and change their form when they are 'processed' so I don't see any reason to believe it would be at all special.
edit: considering the Ark doesn't have a nav sphere, I guess we can assume some natural qualities of the lifeform. It is capable of surviving in a vacuum, it has levitation abilities, it is capable of collecting, storing and diverting massive quantities of energy, though this could be fully dependent on size.
There's no guarantee whether aptom's cells could access any of this information though. The code could be incompatible/exotic, and also, we only have Aptom's own supposition to go on. Based on his monologue, I guess we can assume he has tried absorbing insects or birds or even trees. But I'm not sure we can assume that he is fully considering lifeforms that could have exotic biology. I just don't think we can take it as a given, even considering all this.