how good is integration support with Eclipselink by Infinispan ?
I have no idea. In the case of Hibernate support, it's Hibernate supporting Infinispan, not the other way around. Infinispan doesn't support JPA providers directly just provides a suited API for JPA implementors to use.
So this is a good question for EclipseLink developers.
or do i even need Eclipselink for caching when I have Infinispan ?
That depends on what you want to achieve. If you manage the cache directly but trying to lookup in the cache and put stuff in the cache with your own code you don't need them integrated. In the case of Hibernate 2nd level cache, its usage is mostly transparent so that Hibernate will load data from the cache when possible, keep the cache content in synch, and only hit the database in case of cache misses or queries which are not cacheable.
Still there are many use cases in which you might want to cache some things explicitly via self-written code, in which case a 2nd level cache integration is not needed.
BTW, due to some leagal issues, we can not use Hibernate. We must use Eclipselink for persistence.
That's very sad; I hope your decision makers didn't just read too much FUD and properly understood the Hibernate license: http://hibernate.org/license
For legal doubts it would be nice to contact Red Hat legal department, we strive to be open and if something isn't clear maybe something can be clarified.
I'm puzzled about your legal issue of not able to use Hibernate, even if you're deploying on the JBoss EAP which has the same license. If the problem is that your application needs LGPL code at compile time, did you consider using plain JPA ? Hibernate does of course implement JPA, and is an excellent implementation.