Not only is water a problem for corrosion on adjuster bolts, they can also experience galvanic corrosion. This occurs when two dissimilar type of metals are in contact with one another in the presence of moisture. An electrical process takes place and causes the less noble of the two metals to corrode.
The easy answer to this is to coat the fastners with anti-seize, as Pete has explained. But shop for anti-seize and you will find a plethora of different brands with as many types of make-ups.
With regular maintenance you can probably chose any of the anti-seize compounds available and do fine.
However, by simply coating the bolt threads with a wateproof grease may have you thinking the threads are protected, but they may not be for an extended amount of time.
Grease, in simple terms is oil that is whipped up in with soap base such as lithium, to provide a less fluid lubricant that will stay in place much better than the raw oil would. Lubrication and corrosion protection from grease depends on the oil seperating from the soap base and coating the surfaces.
When we paint on a grease, there will come a time when the finite amount of oil will have seperated, or left the soap base and is no longer present. The remaining soap base is not a good protector against corrosion. In some cases, as in that of grease that is made with a calcium base, the remaining base soap can actually harden up like concrete. Not a good situation.
Many anti-seize compounds, as well as many greases, contain molybdenum, or "moly". The molecular structure of moly works quite a bit differently than plain petroleum oil does. Moly is a polar solid, meaning it is like little molecular magnets that adhere themselves to the oxide layer of the metals surface. They will fill in all the microscopic craters and valleys that are present in all metal surfaces. Even when the base oil has left the carrier (soap), moly will still remain providing continued protection of both the bolt and the reciever threads.
If you are going to coat your adjuster threads with grease, or with anti-seize compounds, regular maintenance will mean you will probably be fine no matter the choice of product. However, if you feel you may take an extended amount of time before you address your adjuster bolts, you should use a grease or compound that contains molybdenum.