Cross posting transactions wouldn't really serve any purpose or make anything easier. The transaction IDs, block IDs, timestamps, order, etc would all be different so the cross-posted transactions would not be usable for anything. IF a move happens, then it will just be such that all transactions before a certain date/time are stored on the Steem blockchain, and after then will be stored on the Hive blockchain.
RE: Splinterlands' Plans for the Upcoming Hive Fork