-can JR rip on RP2 from a usb drive in flac and dump to a temp drive and then dump to an NAS
If you mean "rip from a CD drive," the answer is no. CD Ripping is not supported on Linux yet. Additionally, a Pi is not necessarily a great choice for a CD ripping work station due to power issues (unless you're running a powered USB hub).
-can JR do web radio streams?
Web support is not all the way there in JRiver for Linux. Some folks have had good luck with web radio streams, others have had less good luck. There's a 30 day trial, so you can easily try and see how it works for you.
-can JR support a headless web gui (i saw the thread on hacking one, but i'm hoping that stock now)
The answer to this question depends on what you mean by a "headless web UI."
1) If you mean "can I control playback on a headless pi using an app-style web interface," the answer is yes. Webgizmo is a web app that will run in any browser and can control playback on the Pi from another computer. Additionally JRiver provides the Gizmo app for android for free, and a premium app called JRemote for android and ios that costs money. Any of these solutions will allow you to control playback on the Pi and browse your music library, etc. These have been around for a while and are fairly mature.
2) If you mean "can I reconfigure settings and do library management on a headless Pi remotely?" The answer is yes, but you'll need to use VNC or remote desktop software. There are step by step instructions in my Pi quick start guide here:
http://yabb.jriver.com/interact/index.php?topic=99370.msg687832#msg6878323) If you mean "can I do all JRiver configuration through a web app?" The answer is no. You can control playback through a web app, but serious configuration will require using VNC or remote desktop.
-can JR support streaming services like amazon prime, google play, tidal, etc.?
Short answer: no. The windows version of JRiver has more robust web functionality and a loopback WDM driver that allows it to engage more robustly with streaming services. The Linux version isn't there yet, so there isn't really a convenient way to engage with those services through JRiver on Linux yet.