I have not used Enterprise Lib, so let me talk in terms of log4net and postsharp.
Log4net has great logging stuff, and you can use AOP ( using postsharp ) to drive this logging in a declarative way. In this sense they are great compliments.
Here is an example. I would expect the same to hold true for Enterprise Library based logging or exception handling.
What I wouldn't suggest you use is the two AOP type things together, so the policy injection in Enterprise Library looks like AOP to me, so I wouldn't use it and postsharp.