Proler is a real English word, but one that's not used any more. Whether it's accepted in Scrabble or Words with Friends or other word games is up to their official word lists.
It has no individual entry in OED online, but proler[s] appears in three 17th and 18th century quotations under prowler.
Searching Google Books, it can be found in The Chambers Dictionary (Page 1315, 1998):
prole2, proler Obsolete forms of prowl and prowler.
It also shows up in The Chambers Crossword Dictionary, 3rd edition (Page 96, 201
06 patrol, proler, roamer 07 proller, prouler, stalker 08 tenebrio 09 nighthawk, scavenger
From there it's a short hop over to other (unofficial) Scrabble dictionaries.