May not be necessary, but sure won't hurt. What's the chances that you will want to pull the intake back off in the future? There are a number of good sealers for this job. Which one to use depends on how big a gap needs filled and how difficult it will be to remove the intake in the future.

Right Stuff is probably the best gasket maker I have ever seen. It will fill big gaps and, as the name implies, doesn't even need the paper gaskets. But you may need a crane to pull the intake back off. It is that good. Personally, this is what I use on things that I don't expect to need to come back apart.

High Tack is a good sealant to use on the gaskets. But since it is gasoline resistant, it is a real mess to clean up if you ever need to pull the intake. Have some lacquer thinner or acetone handy for clean-up.

Hylomar A/F is the best sealant if you think that the intake will need to come back off. While it is very good at sealing, it releases the part rather easily. But it is pretty expensive and can be difficult to find. This is what I use on anything that I think may need to come back apart.

And finally grease. Of course grease is not really a sealant, but it softens and helps keep soft paper gaskets and sure makes taking things apart very easy and often allows the re-use of the gasket. For example, I always use grease on my carburetor base gaskets.