As far as I’m aware Rosetta used to be used to install PowerPC applications (Final Cut Studio 1 and 2), but Final Cut Studio 3 (that’s Final Cut Pro 7) is written for Intel processors and doesn’t need Rosetta.
If you were installing Final Cut Pro 6 you might have trouble but FCP 7 should be fine. I did a clean install of Yosemite on my 2014 Retina Macbook Pro, and have installed and used Final Cut Pro 7 with no issues – I even got QMaster working ok.
For anybody getting a new laptop with Yosemite pre-installed I guess there might be some hardware-level drivers missing that disallows FCP7 use but I doubt it.
Hope this helps. Will