If you are referring to custom web services then I cannot think of any option that would allow you to host your own custom services inside of the Jive instance. That is simply not part of the frameworks that are available in cloud.
Since an addon could communicate with the Jive instance your service could be hosted somewhere and could operate like an extension of the Jive API but it would need to use only the Jive API. In this case I would be thinking of something like a posting service that is really just a facade to a set of calls. Not sure there is a big use case for something like that.