"You say to treat memoir as fiction when querying, and that makes sense to me. My concern is, will I irritate agents if I don't follow their specific guidelines for submitting non-fiction?"
When querying, memoir needs to be treated as fiction in certain respects: as with fiction, the entire manuscript should be finished before you query; as with fiction, your concept won't matter as much as the execution of the writing; and, unless you are a celebrity or have a major, national platform, your background and platform won't matter as much. It is more about the writing itself, whereas with most types of commercial non-fiction, greater weight is given to your expertise, the competition, the market and other issues.
Most agents should specify guidelines for submission of fiction, non-fiction and memoir. If they don't specify, then at first you can treat memoir as non-fiction for the sake of initiating a submission. For example, most agents want you to begin with a one page query letter--and in that case, just send in a letter, and if they want more, they should tell you how much they want. If they ask for a proposal, the typical non-fiction proposal contains an overview, an outline and 1 or 2 chapters, and you can send that. Don't worry--these distinctions are not so important, because if they want more, they will tell you exactly what they want. The important thing to remember is that, unlike other types of non-fiction, with a memoir you should not query until your entire manuscript is complete. You don't want to have an agent like the first two chapters and then not have the manuscript ready to show for two more years.