If I had a FireWire 400 DVD drive connected (via a FireWire 400-800 cable) to a FireWire 800 hard drive that was then connected via a Thunderbolt to FireWire 800 adapter to a Thunderbolt hard drive, that was then connected to a Mac, would I be able to use all the drives? And would I get Thunderbolt speeds on the Thunderbolt drive and FireWire 800 speeds on the FireWire drive? Also all the drives are powered externally.
Okay, It just dawned on me I have the hardware here to test daisy-chaining two FireWire devices at the end of the Thunderbolt daisy-chain and it did work. I have access to all devices in the chain, both Thunderbolt and FireWire. I could not test with FireWire devices in the middle of the chain as I'm short a cable/adapter for an in the middle configuration. However Apple has stated in the past the non-Thunderbold devices had to be at the end of the chain.
As to the throughput speed of the FireWire devices they cannot exceed what they're rated regardless of how connected.
Your setup will not work. You must have separate FireWire and Thunderbolt chains, and not connect devices to both interfaces simultaneously.