Here it is from the horse’s mouth:
Thank you for contacting Nik by Google.
The Nik Collection is not currently compatible with the newly release OS X Yosemite 10.10. Please continue to check back with the compatibility section of the help center to find when is compatible here: https://support.google.com/nikcollection/answer/3000889?hl=en&ref_topic=3000839
If you have any further questions, please reply to this email or visit support.google.com/nikcollection to call our Customer Service Department Monday through Friday 8:30 am to 5:00 pm PST.