Replacing ungrounded receptacle with grounded receptacle on metal box
I wouldn't even need a pigtail jumper ground because the green screw has continuity with the 10-32 screw and ears of the receptacle anyway, right? Am I missing anything?


Since they used metal raceways you could do it this way only if the receptacles are of the "self-grounding" type. They are more expensive and have a metal clip on one end of the mounting yoke. Or, if your boxes are surface mount and you remove one of the plastic screw keepers. See (A) below.

Chicago has their own Electrical Code but I would be surprised if it is any more lenient than the National Electrical Code. They are usually more strict. The NEC allows self grounding receptacles to be used for grounding in this article, attention to (B):


  250.146 Connecting Receptacle Grounding Terminal to Box.
  An equipment bonding jumper shall be used to connect the grounding terminal of a grounding-type receptacle to a grounded box unless grounded as in 250.146(A) through (D). The equipment bonding jumper shall be sized in accordance with Table 250.122 based on the rating of the overcurrent device protecting the circuit conductors.
  
  (A) Surface-Mounted Box. Where the box is mounted on the surface, direct metal-to-metal contact between the device yoke and the box or a contact yoke or device that complies with 250.146(B) shall be permitted to ground the receptacle to the box. At least one of the insulating washers shall be removed from receptacles that do not have a contact yoke or device that complies with 250.146(B) to ensure direct metal-to-metal contact. This provision shall not apply to cover-mounted receptacles unless the box and cover combination are listed as providing satisfactory ground continuity between the box and the receptacle. A listed exposed work cover shall be permitted to be the grounding and bonding means when (1) the device is attached to 
  the cover with at least two fasteners that are permanent (such as a rivet) or have a thread locking or screw or nut locking means and (2) when the cover mounting holes are located on a  at non-raised portion of the cover.
  
  (B) Contact Devices or Yokes. Contact devices or yokes designed and listed as self-grounding shall be permitted in conjunction with the supporting screws to establish equipment bonding between the device yoke and  flush-type boxes.
  
  (C) Floor Boxes.......
  
  (D) Isolated Ground Receptacles......


Check with your inspector to see if you are under the Chicago Electrical Code and if it allows this.