There are two connector on the ROCK Pi eMMC module, one is the same connector and signal with ODROID, the other one is only for mounting, it’s empty. So it’s compatible, which means odroid eMMC module can be used on ROCK Pi 4, and ROCK Pi 4 eMMC module can be used on Odroid. Same with the eMMC module adapter board.
But please note that, Odroid has multiple eMMC modules with different eMMC versions(eMMC 4.5/5.1). ROCK Pi 4 has only one eMMC version 5.1. Please check your board if it supports eMMC 5.1.
We haven’t actually tested any our eMMC module on Odroid board, hard to buy here. What we have tested is one PINE64 eMMC module, which is said working with Odroid. The PINE64 eMMC module works without issue on ROCK Pi 4, and the PINE64 eMMC USB2.0 reader works with our eMMC module too.