Re: can I effectively light coals on a hob like this?
you've got to figure that those stoves have been tested with all burners turned on "high" with nothing on them for a period much much longer than it takes to light a coal. products have to be as idiot proof as possible. i believe new ones even have automatic shutoffs which cut the heat before it gets too high to damage the glass top.
back to my original point (which admittedly was a little off track from the OP), coals burn at what? like 350degF and the heating element in the stovetop can put out at least 450-500degF... there's no way that the coal is magically adding heat back to the stove unless it's trapping and accumulating heat underneath it.
other than the potential for a little black smudge that will need to be wiped off later, i personally feel safe doing it.