I'm not a mod, and maybe one will chime in with more detail, but I'm going to say that I think it's okay as long as you do it differently enough from the first person. For example, you could use a different species as the base, or change the markings a bit.
For example, I have this Kuhna:
and Toxic later got this one:
As you can see, they're very different, and I think that's okay and nobody would be mad about it! :3 (There's also a Sylveon Sahound (which Mojave owns) and a Sylveon Phyrette (which I own) so there's a lot of them going around!)
If it were a breedable, like a Lucain, you'd just have to use at least some different markings.
If you're really unsure, you could always ask a mod directly, and/or ask the owner of the pet you're worried about copying.