Can you be an animal rights activist if you feed pet food (which contains meat) to your cats and dogs?
Can you be an animal rights activist if you're an animal and your diet includes eating other animals?
Of course you can.
Can I become an animal rights activist even though I eat their products?
You can be against animal testing and still eat meat, eggs, ect. But if you then use products (e.g. Cosmetics products) where you know animals have been tested on... Well, it's a bit oxymoronic. If you say it's wrong to eat animals, but you continue to eat meat, that's not gonna work either.
If you say it's wrong to do something, you can't then do it yourself.
Basically, practice what you preach.