The rules say "Unmodified hit rolls, wound rolls and saving throws of 1 always fail. Unmodified hit rolls and wound rolls of 6 always succeed."
The rules are unclear what unmodified means though. Is it meant to be plays that a 1 showing on the die always fails regardless of any modifications that may apply to the roll. OR does a die roll of 1 that is subject to being modified by a rule (like +1 to save rolls from light cover) succeed if the
Sv characteristic is 2+.
I think it is clear that the intention is that (to use a different term) that a natural 1 always fails and a natural 6 on hit and wound rolls always succeed. I really wish that was the wording of the rule if that is the intention.