No, but they can use their Bennies to re-roll at any time. Some Savage World books allow any spend of a Bennie to auto succeed at 4 so you could allow an auto fail too but it would be a House Rule. I would allow a player to spend a Bennie to auto-fail it make sense and fit in with the SW Motto of FFF.

No, the must joins the phrases. You must make a Smarts roll or go Berserk; mean you have to roll. The results determine if you go berserk. This is a standard lazy English way of writing this. Other interpretations lead to madness. It does not make logical sense as there are missing brackets and lawyers and programmer would argue about the laws of precedence but in normal English its meaning is clear.

if( wound )
    {
    roll = smarts check;

    if( roll < 4 )
        {
        berserk;
        }
    }

But they can use their Bennies to re-roll at any time. Some Savage World books allow any spend of a Bennie to auto succeed at 4 so you could allow an auto fail too but it would be a House Rule. I would allow a player to spend a Bennie to auto-fail it make sense and fit in with the SW Motto of FFF.