Yeah, what you'd really want is an OSGi bundle that launches the Zookeeper Service from within the OSGi Framework. It should be configurable through the OSGi Configuration Admin Service and support changes in configuration after the server was launched.

An initial attempt to provide some of this functionality has already been done in the context of ZOOKEEPER-425. Look at the Activator.java and ManagedService.java of zk_patch3.patch in that bug.

For the moment I put the bundle that runs the zookeeper server in the CXF-DOSGi codebase (because I'm using the functionality there).
It can configure (through the OSGi Configuration Admin Service) and run Zookeeper Server.
Reconfiguration is also supported (just change the configuration information on the PID: org.apache.cxf.dosgi.discovery.zookeeper.server and the reconfiguration is applied by shutting down and starting up the zookeeper server in-process.

You can find it here: http://svn.apache.org/repos/asf/cxf/dosgi/trunk/discovery/distributed/zookeeper-server

Let me know when you think the zookeeper codebase is ready for this. It works for me, but I understand that the general feeling is that some changes need to be made to the zookeeper core before something like this can be accepted.
I'd be happy to contribute this to zookeeper if you like to have it.