It will not be supported. Maybe it will work; maybe it won’t.
That said, your best bet to get it working is with a clean install of the operating system. An inplace upgrade is a recipe for disaster.
Why do you need to upgrade to Yosemite? I have InDesign CS5.5 on my Mac running Lion, and although I've received a notification saying that I can upgrade to Yosemite, I'm not bothering. Is there something specific in Yosemite that you need?
Actually, the question is whether MacOS 10.10 is compatible with CS5.5, an existing application. Alas, when you are running MacOS, you pretty agree to an environment in which an OS upgrade may force application upgrades simply because Apple purposely does not maintain compatibility with existing applications. Sad, but true. Nothing that Adobe can do to get around this.
And more to your original point, Bob Levine is correct. It is not officially supported on MacOS 10.10 and even if you can coerce it to install and run at all, you will definitely have a compromised experience.
I downloaded Turbo Tax 2014 and it won't run on 10.6.8. I'm perfectly satisfied with the CS5.5 suite.
Then you have a choice to make.
You could try to install 10.7. Or what are the minimum requirements for Turbo Tax?