What would happen if I connected a dishwasher to a hot water supply line?
The Siemens SK26E220EU manual says:


  Water temperature: cold water preferred; hot water max. temperature 60 °C. 


Which appears to imply that it is fine so long as the hot water is no more than 60C at input. It includes a water softener, so it may well have some parts in the water path before it heats the water hotter that would be damaged by hotter water. If your hot water is electrically heated, it makes little difference to your overall operation cost - if you have an alternate, less expensive source of hot water, you'll benefit, so long as it's not too hot.

For other models, check the manual - or just hook it up to cold if you are electrically heating your water anyway.