Yep, I've tried it DV25, DV50, 720 & 1080. You do need Raylight (darn useful thing anyway). Also edited the sequences using media on the camera via USB2. Pretty slick.
Raylight is kinda a funny plug-in. It runs as a background application that allows native mxf editing in a bunch of editing systems. Go to dvfilm.com for more info, I bet they have all of the answers to your questions.
It can, but doesn't have to, run in the background. Basically it creates Quicktime reference files that "point" to the various MXF files. Once it's processed a set of MXFs, you don't need Raylight any more. In fact, you could uninstall Raylight & still edit. Note that the QT ref files are created almost instantly and are VERY small in size.
And yes, you can drop a single clip or a fully edited sequence (with any effects, layers, audio, etc) onto Raylight's "P2 Maker", and out comes a MXF set. NOTE: it will *not* span cards, so you're limited to card size if you're exporting to a card.
I still think this is the coolest thing, that you can show up with just your camera & a MacBookPro, shoot, edit, and play out HD-SDI.... all with *no* importing/digitizing. Already had a chance to use this workflow once "for real"... the sat truck op thought it was pretty cool as well (especially since he had no DVCProHD playback deck).
This can easily be done on an HVX without the use of Raylight, I'm surprised you can't do the same with and HPX. I've done this a couple times with my HVX. Here's a thread about it.