I can confirm that. APT-X is currently not working in OSX Yosemite. My Arcam RBLink is connected via AAC. No way to get it to work in APT-X mode.
To add some quick observations with aptX codec enabled, I am noticing no lag whatsoever in changing tracks, volume changes or switching between audio sources i.e. iTunes, Safari and so on.
It certainly has made my experience much better than what I have had before. That in itself is more than enough for me, but as aptX is considered a hi-fi codec when it comes bluetooth streaming is an obvious plus.
But overall, smoother experience, no jerking audio and cutting off.
I just noticed on Yosemite 10.10.2 (14C78C) that aptX is working now. I've always been getting AAC forever. It is actually the time I have ever seen aptX.
I haven't seen this documented or noted anywhere else.
Gosh I sure hope they release 10.10.2 soon. Got a new set of Beats studio wireless and would love to connect apt-x.