I'm not sure about the bitlocker portion. I would be very careful with moving any encrypted data around. If possible, I would disable encryption before moving an encrypted drive to new hardware. You should review documentation about the encryption method you are using before moving the drive.
Disk migration from the H700 to the H710 is supported. I don't think disk migration in the other direction(newer to older) is supported. Supported disk migration should be covered in the manual of the newer controller.
Even though it is not supported, it will probably work. It is best practice to make sure both controllers are using the latest firmware before performing disk migration.
Dell EMC, Enterprise Engineer
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