I ran across this JVM configuration on a server recently. I should note that the server in question was having some issues, so this is not an endorsement of this approach. I simply had not seen this sort of configuration on a Coldfusion server before. Here are the JVM arguments:
If you have ever used the Coldfusion Administrator to change garbage collectors you may have run into the issue where Coldfusion adds the UseParallelGC garbage collector back into the arguments. For example, if you change the garbage collection to "UseConcMarkSweepGC" and then update (again - using the Coldfusion Administrator), you will end up with both the UseParallelGC and the UseConcMarkSweepGC as arguments to the JVM. When you restart Coldfusion it will fail - complaining that it cannot handle 2 separate GC arguments. See this previous post for a more thorough discussion of that issue.
However, this does not mean that all garbage collectors are mutually exclusive. In my reading I missed that tidbit. The arguments above show how they can be made to live together. After a bit of googling I found several warnings that explicitly tell me that "UseConcMarkSweepGC" and "UsParallelGC" are indeed mutually exclusive. Since that is the error I ran into I suppose I jumped to the conclusion that GC's are mutually exclusive in general. Now I know that this is not always the case. Note also the CMSParallelRemarkEnabled switch in the example above. This switch is designed to reduce the pauses that occur when the GC is marking objects for deletion.
In my searching on the topic I found this document in the help files for CAMS (a network security policy server from Cafesoft which runs on Java). While some of the advice is specific to CAMS, I found the overview to be excellent. In particular there is some good information about the differences between multiprocessors and single processor machines - and why various garbage collectors work or do not work well with them.
I know there are some Java/Coldfusion gurus reading my blog. Perhaps you could chime in with some additional information.