ConvertAvroToORC in Apache NiFi uses Apache Hive 1.2.1, which is not guaranteed to be compatible with any Hive 2.x release, although it's nice to know that it works fine with 2.1.X. The NiFi in Hortonworks Data Flow (HDF) uses HDP Hive, which is 1.2.1 plus many additions. This is also not guaranteed to be compatible with any Hive 2.x release, but it may just happen to work for you.
In the future, I presume there will be a set of Hive/ORC processors that use Hive 2.x rather than Hive 1.x. However, an Apache NiFi release will still be using Apache Hive / Apache ORC libraries, so it still might not work with a vendor-specific version of Hive. Again the exception is HDF NiFi, which supports HDP Hive.