The simple answer is no. An offer letter confirms the terms of the verbal agreement by the hiring company. At the very least, it should include your position title, starting salary, bonus potential, start date, reporting relationship, and an outline of benefits.
In extreme situations, there can be unforeseen extenuating circumstances that have nothing to do with you that might prevent the hire altogether. Verbal offers can be withdrawn.
There may be details that catch you by surprise that were overlooked ...