I don't see why darwinian evolution would necessarily create humanoid aliens in other environments-- sure arguing that they are likely to have structures similar to eyes to take advantage of EM waves makes sense, and even arguing that they'll have a structure similar to a head where a centralized sensory-decision-making unit like a brain exists makes sense, but walking on two legs? Even looking at the more intelligent life-forms on our own planet we find a great diversity of structure: from apes to dolphins to elephants to octopi... All I'd say we can really gather from this argument is that aliens will look like creatures and not like flickering light rays or crystals or something incomprehensibly foreign.