Yes, DESIGNER is a Scrabble word!

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

Is it a valid word?

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

a person who specializes in designing architectural interiors and their furnishings
someone who creates plans to be used in making something (such as buildings)
someone who specializes in graphic design
a person who devises plots or intrigues
someone who designs clothing

Also: interior designer, interior decorator, house decorator, room decorator, graphic designer, fashion designer, clothes designer.