You shouldn't have any Linux-related issues with it, ADAT will only be used to communicate between the Scarlett and Saffire.
The only issue you might run into is clock sync: If your Scarlett is your main interface (connected to your computer), and you are running an ADAT cable from the Saffire to the Scarlett, then the Saffire won't have a clock to sync to, so you'll need to run a second cable - e.g. another ADAT, Word Clock (BNC), or something to send clock sync to the other device.
If your second device isn't synced you'll probably hear pops and cracks in the audio coming from it. And, if you absolutely can't get another cable for whatever reason, you can switch the clock master to the second device in your DAW or on the device itself.
Basically, what tasankovasara said, but with a few more details, mostly to underline how important clock sync is. And my experience is the same as theirs - a cable for sound, a cable for clock and it just works.
Also, if you go into a store and ask for ADAT cables and they look at you like you're from the moon, they're also called Optical Cables.
I don't know of an "out-of-the-box" distro for multimedia outside of Ubuntu Studio, but I do know of a utility that will turn any distro into a low-latency, pro audio setup: rtcqs - it runs 10-12 tests on your system and tells you how to set it up for realtime audio, if it isn't already - this is very much NOT what you asked for, but if you get your system going but it's not performing like you expect, this could be the thing that fixes all your issues.
I'm going to add Broadcom to your list, but otherwise it is a great, concise explanation of the root issues behind why some users will struggle with older hardware while others will have no issues.
You shouldn't have any Linux-related issues with it, ADAT will only be used to communicate between the Scarlett and Saffire.
The only issue you might run into is clock sync: If your Scarlett is your main interface (connected to your computer), and you are running an ADAT cable from the Saffire to the Scarlett, then the Saffire won't have a clock to sync to, so you'll need to run a second cable - e.g. another ADAT, Word Clock (BNC), or something to send clock sync to the other device.
If your second device isn't synced you'll probably hear pops and cracks in the audio coming from it. And, if you absolutely can't get another cable for whatever reason, you can switch the clock master to the second device in your DAW or on the device itself.
Basically, what tasankovasara said, but with a few more details, mostly to underline how important clock sync is. And my experience is the same as theirs - a cable for sound, a cable for clock and it just works.
Also, if you go into a store and ask for ADAT cables and they look at you like you're from the moon, they're also called Optical Cables.