Is there a resource that lists what can and cannot be used in Actions?
Yeah read that, and the line "To tell which tasks cannot be recorded, watch the Actions panel: if the name of the command or tool doesn’t appear after you perform the task..." so basically do it and find out if it's doable, which if it's a multi-item action can be a pain when you find one that won't work.
If you are looking for a detailed register that may tell you what definitely is actionable and what definitely is not: I don't think that something does exist in this regard.
A rough rule of thumb is that more recently introduced features/commands are not actionable, whereas almost all "traditional" features can be recorded.
Unfortunately, the entire action mechanisms in Illustrator have been neglected for many years.
Thanks Kurt, figured as much.