When installing a 14-30R dryer receptacle, do I need an additional ground connection to the box?
Metal boxes must be always be grounded.
For a surface mounted metal device box NEC 250.146(A) allows omitting the jumper to the device if the yoke mounts flush and at least one paper washer is removed or omitting the jumper if using a cover mounted receptacle if the cover and box are &quot;listed as providing a satisfactory ground...&quot;.
Really the Code paragraph is a little long and detailed, if you wish to omit the jumper between box and receptacle I suggest you find a quote of NEC 250.146(A) or read it directly on the NFPA website.
Edit: The Hubbell product page for the 810C indicates it meets the requirements of the NEC Article 250.146(A) that allows connecting the ground only to the box.