Strangely, colors in PS and LR match today when viewing these two files. I have no idea what is going on here; I made no changes to PS yesterday or today, only opened and viewed images.
To answer your questions, the files were TIFFs in both LR and PS and they were rendered using Lightroom's Edit in Photoshop command (edit a copy with LR adjustments). Though the DNG vs the TIFF in PS showed the same color mismatch. As far as compatibility, I don't know. Is there an incompatibility with LR3 and PS CS3 Camera Raw versions?
I will try again to recreate this issue and get back to you. At the moment, all is well but I'd really like to know what it was that I did to cause this weird behavior.