This is a bit of a dumb question... and admittedly so.
I understand that things can be lethally radioactive without being thermally exciting. (say for instance, rapidly decaying gamma emitters, or highly bio-absorbed materials like radioactive iodines) However, that does not sound like what is being discussed here. It sounds like they are discussing the crud left over from spent fuel rods, or the crud left over from centrifuging yellow cake uranium, and pals. In those cases, the material emits radiation of kinds that ARE thermally exciting.
In which case, (unless it decays SOO rapidly that containment is a very serious issue), casting it into a glass containment block, and using it as a radioactive heat source for space probes looks like a potentially beneficial way to get rid of it. Not everything you would put an RTG into needs to have humans around it. (but yeah, electronics dont like high energy particle bombardment either.)
As for the "I am TRUMP! I SMART! I save money by reclassifying glowing glass bricks the same way I classify dirty radioactive gloves, so I can just put it in a hole with some dirt on top!" Yeah, that is pretty much what this appears to be.