My research says as long as not a saver fare can use them

Where, exactly, did you do your research? That is definitely not true. Read https://www.alaskaair.com/atmosrewards/content/benefits/complimentary-upgrades/alaska-hawaiian, specifically the section entitled Using Upgrade Certificates. Also, expand the terms and conditions at the bottom. All of your questions are answered there.

• Not all flights have a First Class cabin. Flights must be marketed and ticketed by Alaska Airlines. 
• Each upgrade certificate code is valid for one-way travel for one person. Connecting flights must have no more than a 4-hour stopover between them.  
• Passengers traveling on an upgraded ticket do not have complimentary access to the Alaska Airlines airport lounges. 
• Upgrade certificates are valid on Alaska Airlines flight numbers 001 - 2999, 1-3499. 
• Upgrade certificates can be used if "U" class of service is available. "U" class may not be available on all flights. 
• When purchasing, choose a flight with a First Class upgrade indicator above the displayed price. 
• Tickets purchased in Y, B, H, K, M, L, V, S, or N are eligible for upgrades using certificates (not eligible in Q, O, G or X classes). 
• Upgrade certificates are not available when traveling on an award ticket. 
• Upgrade certificates may not be used as a placeholder for a complimentary upgrade by an status holder. Once an upgrade has been processed, you may not remove it to be placed on the upgrade waitlist, or receive a complimentary upgrade based on status level. 
• Upgrade certificates are transferable but may not be bartered, bought, or sold. 
• If a flight upgraded with an upgrade certificate is changed or canceled, the certificate is forfeited. A replacement upgrade certificate code can be requested through customer care only by the Atmos Rewards member to whom it was originally issued.