No it's a universal limitation: a non-High Speed -RW drive won't burn a High Speed-rated -RW disc. The same is true regarding Ultra Speed discs and earlier drives, as well: can read but won't write at all. I don't know for sure what's different technically but quick reading suggests it's a difference in laser write output and/or chemicals used in the disc dye across the various generations.
I don't use -RWs a ton but I have a small stockpile of older discs should I need them. It's not easy to find the early -RW discs anymore without mail-ordering some NOS discs or buying from special vendors. Sometimes you'll get lucky at a thrift store.
I also soldered in a pin header to use the SE/30's LED with my SCSI2SD. I compared mine side-by-side with my Quadra 700 and though there's some age difference the power LED on the Quadra is definitely green and the activity LEDs are, near as makes no difference the same, and definitely yellow/amber.
Yeah looks like I got some bad info on that and jumped to the wrong conclusions. Sorry. Definitely no PCIe signals available at the AirPort Extreme socket in a late 2005 G5.
However if all you wanted was internal BT the rest of my post stands: you can just trace out the 5-10 USB lines and install a USB connector rather than run all of the unnecessary lines and find the special connector and then an adapter for whatever BT module you were planning to install.