Scope doesn't immune you to suppression ,nor unlimited vet spawning but it gives you perfect accuracy(intended)
Its not an exploit but it is a bug in the fact you can toggle the scope to ignore the suppression effect. If you start to get the effect you only need to unscope and then scope back in to reset it. That is where the issue comes in and needs to be fixed.
Being completely fair, they nerfed the range of the skull to 12m, so it basically no longer buffs the damage for incoming attacks unless you're within spitting distance of the skull.
It's not Just Eldar that has worst suppression resist , it's just because Shuriken canon has higher RoF and therefore does more suppression but yeah suppression resist should be much lower