Can you link Local Service Ads to GBP's that are "service area" businesses? I think an address needs to be displayed on GBP to be linked, if anybody can confirm that would be excellent. It looks like information online is limited on this.
Just for clarification, I'm assuming you mean linking for review sharing purposes? Otherwise, Google doesn't require you to have a GPB to run Local Service Ads.
You are correct, it doesn't appear that there is anything specific about the type of GPBs that are allowed to be linked to your Local Ads account, which seems to imply that you should be able to, otherwise it would be specifically mentioned that only GPBs with visible address are allowed. However, I personally can't confirm this is the case as we haven't setup any SABs on LSA. @BenFisher and @TomW are experts in this area, hopefully one of them will share their knowledge and answer your question .
From what I recall a SAB can be used.