Are any of the plastic pipe support clamps approved for use with hydronic systems?

Yes. All Oatey plastic pipe supports are approved for this application, but you should    confirm the maximum temperature that the pipes will reach when in use. With the    exception of the DuoFit Pipe Clamps rated from 0°F to 230°F and the Stand-Off Half Clamps rated from -60°F to 160°F, all other Oatey plastic straps are rated from 0°F to 180°F.