Sorry, but that is not how their blood functions.
"Acid" is just a property of an element, mixture, or compound. All it means is that the substance's pH is low, making it acidic. It does not provide a source of energy.
Acids are caustic because their low pH makes them break down and destabilize other substances. A xenomorph still has blood, and their blood functions in a similiar way to our's.
Their blood simply has a very low pH, causing it to be acidic. This fact does not interfere with their internal functions, but can be extremely hazardous to the outside environment.
And thus I clothe my naked villainy
With old odd ends stolen forth from holy writ
And seem a saint when most I play the devil.