I am not familiar with the weapon, but i can't see that a cracked flash hider should make a great difference to the accuracy of the weapon. If I were using it for Olympic competition, I would have it replaced, but for all other use , NO.
I would however keep an eye on the crack to ensure that it is not getting worse, and I would replace it at the first available opportunity, but merely for cosmetic and possible safety reasons.
I lost the flash hider off an SMLE No5 Mk1 Jungle carbine years ago and was unable to get another. I bodgied one up on the lathe and welded a sight base to it as it is also part of the front sight. It happened at night and we had driven several miles before I realised it was gone, (on my next shot) we went back and looked but could not find it.