I think it should be better to keep them using separate caches, still it's easier for many cases in which top efficiency is not required to allow this.

Today this configuration is not allowed, you would get an exception similar to:

java.lang.IllegalArgumentException: Indexing only works with entries keyed on Strings, primitives and classes that have the @Transformable annotation - you passed in a class org.infinispan.lucene.FileListCacheKey.