There are more than a few spelling variations on the name but all of them (seem to) boil down to the present-day O'Malley or Malley.
I think that it all comes down to who is pronouncing it and which sort of "accent" they're saying it with. Thus, 'O'Malley', spoken with an Irish accent from some particular County, will sound to our ears as 'O'Mealy' and then get transcribed that way.
Another interesting variant is 'Maille'. Oddly, there's even a French mustard company with that name. I'd be curious to know how that connection might have happened.
So, to answer your question, yes, 'O'Mealy' is another variant of the name.