Yes, COMMISSIONS is a Scrabble word!

Letter values in Scrabble US: C 3, O 1, M 3, M 3, I 1, S 1, S 1, I 1, O 1, N 1, S 1.

Is it a valid word?

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

a special group delegated to consider some matter
a fee for services rendered based on a percentage of an amount received or collected or agreed to be paid (as distinguished from a salary)
the act of granting authority to undertake certain functions
the state of being in good working order and ready for operation
a group of representatives or delegates
a formal statement of a command or injunction to do something
an official document issued by a government and conferring on the recipient the rank of an officer in the armed forces
the act of committing a crime
a special assignment that is given to a person or group

Also: military commission.