Tons of hoods have vents... Mine is fine and previous cars of mine have had similar hoods. It'll be fine. It's hot under the hood and will kill any driplets. If it's RAINING BUCKETS under your hood, you could always seal it off, but isn't your motor pretty sealed up from external sources as it is?
In summary, don't worry about it..
Here's a crappy iPhone pic of my set up... I love the hood.