Yes, HIPPOCAMPI is a Scrabble word!

Letter values in Scrabble US: H 4, I 1, P 3, P 3, O 1, C 3, A 1, M 3, P 3, I 1.

Is it a valid word?

HIPPOCAMPI is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a complex neural structure (shaped like a sea horse) consisting of grey matter and located on the floor of each lateral ventricle; intimately involved in motivation and emotion as part of the limbic system; has a central role in the formation of memories
seahorses

Also: genus hippocampus.