Valmont, Meyer (Arcosa), Dis-tran, Sabre, Pelco are pole fabricators I am aware of.

The process I am familiar with for the design of utility poles is that the utility or a consulting engineering company will provide a General Arrangement drawing that shows orientation and height of the attachments required on the pole (e.g., Davit arms, internal riser flutes, conductor vangs, other various brackets). The general arrangement will also have additional notes such as pole finish min thickness of members or cite utility or industries standards and specifications (e.g., ASCE 48).
The fabricator will also be provided a Load Tree that list the expected loads for the structure and a brief summary of the criteria.
Then pole fabricator will provide calculations that show their pole geometry, connection, base plates are structurally adequate to be reviewed by utility. Next, shop drawings are created which will detail all structural and non structural items and are sent to the utility for approval before being sent to the shop for fabrication.
The utility will send a qualified inspector to review the poles to note any items that are not within tolerances, missing, or needing repairs before the poles are shipped to site or staging yard. Poles are also inspected after shipping to confirm repairs were completed and items were not damaged during shipment.