Hello student. First I will go for 2nd question of yours. Cat preperation would definitely be useful for you when you attend or give any interviews in terms of aptitude.

Cate preperation is the highest level for the preperation of aptitife. So for a company's interview purpose, to clear the first round of aptitude, cat exam preperation is more than enough

In answer to your next question, the certificate and the score will be useful, but again depends on which interview you are attending to. If you are attending for a software interview, they can take it, but not a major one. It would just be a mere added incentive