Yes, REGULAR is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, G 2, U 1, L 1, A 1, R 1.

Is it a valid word?

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

in accordance with fixed order or procedure or principle
often used as intensifiers
conforming to a standard or pattern
regularly scheduled for fixed times
in accord with regular practice or procedure
occurring at fixed intervals
relating to a person who does something regularly
(used of the military) belonging to or engaged in by legitimate army forces
(of solids) having clear dimensions that can be measured; volume can be determined with a suitable geometric formula
not constipated
symmetrically arranged
not deviating from what is normal
officially full-time

Not playable in Scrabble US: UNCONSTIPATED.