Hi - I can answer this one...
The silver matte (frosty top, or whatever they're called) is just a smooth matt coating on top of the DVD-R. It's not as rough as a printable disk, which is required for ink-jets to print on.
I use the silver matt disks all the time - fine to write on with a sharpie.
In fact - its so smooth, that if you have a thermal CD printer (e.g. TDK CD Printer), it produces good quality prints. Which is why I buy them.