Even if you get water on the engine its not a major issue a little bit of water wont hurt, but water in the valley will cause miss fires, a daily with a vented bonnet is fine with a genuine nismo bonnet thats what they make it for, so no major water gets into the valley.
If your just going to seal off the vents then also think about the pools of water youll get in the vent area which will also be annoying, been there done that.
Seriously get water channels built into it or get a proper nismo bonnet otherwise go std, they are the only options, blocking off the vents makes it annoying and totally gay