This is indeed H. ustulata...in fact, it keys unequivocally in Townes(1)(1957) to subspecies H. u. ustulata.

First, note that this is indeed Hemipepsis, since the apical end of the vein ("r") bounding the marginal cell meets the wing margin at a right angle in your specimen; and also the 1st recurrent vein (1m-cu) meets the 2nd submarginal cell at its distal end.

To interpret the details of the preceding sentence, see the labelled posts below:

   

Next, note this is a male...from the relatively straight, thick, antennae with 11 flagellomeres.

Then, consulting the key for male Hemipepsis on pg. 32 of Townes(1)(1957), first note that the wings are orange (eliminating H. mexicana).

Next, referring to the labelled wing venation diagram on pg. 7 of Townes(1), note that the nervellus of the hind wing in your photo is indeed almost exactly 0.6 the average width of the "submedian" cell of the fore wing, or nearly equivalently, the "submedianellan" cell of the hind wing). This takes us to species H. ustulata.

Finally, the basal infuscation pattern on of the wings in your photo matches perfectly with that described for subspecies H. u. ustulata in the last couplet of Townes key.

Note also that your location here is well within the "densely dotted" south central AZ area on the range map for that subspecies given on pg. 36 of Townes.

Moved from Tarantula Hawks.