Of course we could tell if it was life or not if we studied it. Life exhibits certain traits and we can observe those traits.

From Wiki
>>Life is a condition that distinguishes organisms from non-living objects, such as non-life, and dead organisms, being manifested by growth through metabolism and reproduction. Some living things can communicate and many can adapt to their environment through changes originating internally. A physical characteristic of life is that it feeds on negative entropy.[1][2] In more detail, according to physicists such as John Bernal, Erwin Schrödinger, Eugene Wigner, and John Avery, life is a member of the class of phenomena which are open or continuous systems able to decrease their internal entropy at the expense of substances or free energy taken in from the environment and subsequently rejected in a degraded form (see: entropy and life).[3][4]

Whether it is carbon based or chlorine based or silicon etc, is a bit of an irrelevancy. With billions or trillions of planets out there, there is room for all possibilities, but if easy interstellar travel exists, the ones with similar requirements to ours would be the most likely to interact with us. What would be the point of them taking people aboard for a good old anal probing if the probees could not survive the ships life support?