Quick Question: would you.....?

A legit agent isn't going to do that. If he reps self-help books, then he's likely got more than one client with a book out, so the conflict is only in your head.

Unless the best-seller is : The Joy of Living with Your Yorkie

and your book is: Yorkies for Life: Little Dogs are the Best

you aren't going to have a direct conflict with another self-help book. It's a broad category.

The worst he can say is no.

Agents generally rep books they know how to market. So in fiction, you'll have agents who rep SciFi, or Romance, etc. Therefore, you'd send your SciFi and Romance to these agents. Yes, they already have many SciFi and/or Romance writers as clients. Yes they are on the lookout for more.

This is because an agent sticks to a subject/genre they know and for which they have publishing contacts. That makes it a little easier for them to sell the ms they represent.

So, if an agent has a good track record of selling as an example spiritual self-help, or cookbooks then this agent will want to see queries for spiritual self help, or cookbooks.

Yes, query the agent in question, and query widely as many agents as possible.