Yes, IRONSIDES is a Scrabble word!

Letter values in Scrabble US: I 1, R 1, O 1, N 1, S 1, I 1, D 2, E 1, S 1.

Is it a valid word?

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

English general and statesman who led the parliamentary army in the English Civil War (1599-1658)
a man of great strength or bravery

Also: oliver cromwell.

Not playable in Scrabble US: CROMWELL.