No Title
Yes.
Employment letter is to show:
(i)you will be engaged in the type of work for which your I-140 (EB1-EA) was approved,
(ii)you will be employed so that you will not be a public charge.
The letter has to describe your job (mentioning whether it is permanent/full time, type of work performed etc.) and does not have to be a special offer letter.
Hope it helps.