Not sure which bushing you are talking about specifically, but I am going to guess most likely rubber. Personally, I wouldn't go around lubing the heck out of all the bushings just yet, try to isolate the squeak first and then correct the exact problem. Most of the suspension bushings that did not come lubed from the factory don't need to be lubed up periodically either, so you might just end up masking the problem temporarily
if i cave i'll give a light spray down on the bushings underneath and see if it solves the problem. i'll go bushing to bushing and check them to see if theres any premature wear from doing alot of water crossings.