On the constraint equations in Einstein-aether theories and the weak   gravitational field limit
  We discuss the set of constraints for Einstein-aether theories, comparing the flat background case with what is expected when the gravitational fields are dynamic. We note potential pathologies occurring in the weak gravitational field limit for some of the Einstein-aether theories. 
David Garfinkle, James Isenberg, and Jose M. Martin-Garcia
gr-qc