It is possible to put ESP to Linux MD array with metadata 1.0 (meta data at the end of partition).
While it might have consequences like mismatched data if system firmware modifies contents
of partition, as firmware most likely unaware about any Linux MD metadata and RAID1 participation,
but this situation is quite rare and periodic array checks and syncing can fix this enable this by default to benefit from fault-tolerant boot on server systems with two disks dedicated for operating system.
It is possible to put ESP to Linux MD array with metadata 1.0 (meta data at the end of partition). While it might have consequences like mismatched data if system firmware modifies contents of partition, as firmware most likely unaware about any Linux MD metadata and RAID1 participation, but this situation is quite rare and periodic array checks and syncing can fix this enable this by default to benefit from fault-tolerant boot on server systems with two disks dedicated for operating system.
Additional information can be found here