Are there calf/soleus/achilles injuries that cannot be picked up on MRI/CT without contrast?

ExertionCompart synd. Exertional compartment syndrome may not be identified by CT/MRI. This is evaluated by compartment testing with activity.
No. The only way a pathology would not be pick-up is to small off imaging slices. If you have a lesion that is 5mm, but your slices are 10mm, the lesion would be missed. MRI would be used for soft tissue and the CT would be used for bone.