Yes, REALISING is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, A 1, L 1, I 1, S 1, I 1, N 1, G 2.

Is it a valid word?

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

earn on some commercial or business transaction; earn as salary or wages
convert into cash; of goods and property
expand or complete (a part in a piece of baroque music) by supplying the harmonies indicated in the figured bass
make real or concrete; give reality or substance to
be fully aware or cognizant of
perceive (an idea or situation) mentally

Also: take in, pull in, bring in.

Not playable in Scrabble US: ACTUALISE, AGNISE.