What evidence supports the use of bone stimulation dev. For delayed union fracture? My friend's 'expert' ortho [austrian] claims they are useless.

Disagree. There is good data that supports the safety and efficacy. Check out orthofix.Com.
Electrical and . Electromagnetic (em) fields are assumed to play a role in bone healing through the same principles as mechanical stress applications. When mechanical load is applied to bone, a strain gradient develops. [4] subsequent pressure gradients in the interstitial fluid drive fluid through the canaliculi from regions of high to low pressure and expose osteocyte membranes toflow-related shear stress, read.
Lots. He needs to read all the literature on this(hopefully there is reading capability in austria).