Simple Uniform Hashing Assumption and worst-case complexity for hash tables
I think the answer is no, SUHA does not imply anything regarding worst-case time complexity.

The bottom line is that


the hashing is (even though uniform) still viewed as random, and
the keys are unknown.


Regardless of how small the probability is for all keys to hash to the same bucket, it's still a theoretical possibility, thus the theoretical worst-case is still O(n).

When discussing hash tables and complexity, I think this is mentioned briefly, regarded as irrelevant in practice and then the discussion moves on to expected run time complexity, and we're in O(1) land.

With the assumption mentioned in the question...


  The difference between the largest and smallest bucket is bounded by a constant factor.


...(which is strictly stronger than SUHA) it can indeed be shown that the worst-case run time complexity is O(1). This assumption implies that even the largest bucket is within a constant factor of the load factor limit. This in turn means all linked lists are bounded by a constant and we get O(1) as worst case.

This assumption however is somewhat unreasonable. While it's quite probable that it holds true for any descent hash function and non-pathological set of keys, how would one guarantee such property? One would have to push this assumption further down and make constraints on what keys are allowed to be stored in the hash table and so on. This is what makes it unreasonable in a sense.