Is either a word in the Scrabble Dictionary

Yes, either is playable

...and is worth 8 points.

Found in the following dictionaries

Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)

"Either" Definition

adjective

Any one of two; one or the other: Wear either coat.
One and the other; each: rings on either hand.
Being the one and the other of two .
Being the one or the other of two .

pronoun

The one or the other: Which movie do you want to see? Either will be fine.
The one or the other .

conjunction

Used before the first of two or more coordinates or clauses linked by or: Either we go now or we remain here forever.

adverb

For that matter .