There are some dialect words in the OED, but by no means all words used in all dialects are in the Dictionary. As the preface to the 2nd edition says: "... a dictionary has definite limits: lexicographers must, like naturalists, 'draw the line somewhere', in each diverging direction. They must include all the 'common words' of literature and conversation, and such of the scientific, technical, slang, dialectal, and foreign words as are passing into common use and approach the position or standing of 'common words', well knowing that the line which they draw will not satisfy all their critics".
Below are some nice dialect words from the OED, together with their definitions. I didn't scour the Dictionary for these; I found them in Chapter 7 of The English Language by Robert Burchfield. Whether they are 'common words', as mentioned above, is a moot point ... Some of them are included because they have, or had, other meanings in Standard English.
ran-tan: to condemn and humiliate (a husband) publicly for beating his wife, typically by causing a disturbance outside his house by beating pots and kettles, singing and chanting loudly, etc., and sometimes also by beating him, chasing him from the town or compelling him to ride the stang. ('Riding the stang', by the way, is defined thus: to be mounted astride of a pole borne on the shoulders of two men, and carried through the streets for the derision of the spectators)
piggle: to fiddle or toy with
pit yacker: a coal miner
pussivanting: fussing, meddling
scrunty: stunted, shrivelled
The aforementioned book chapter only looked at words beginning O to S, so there are no doubt plenty of other delightful dialect words elsewhere in the Dictionary.