You are conflating a number of different topics.
1) Agents who are authors: Would you REALLY turn down Laura Rennert, for example, one of the top agents in the business, because she is also an author? REALLY? If so, I don't know what to say. Good luck.
2) Agents who are also freelance editors "for hire" -- now this is a different kettle of fish. If they are a freelance editor for hire as well as an agent, in my opinion, they might be
going against the AAR canon of ethics. So unless they have a very stringent policy on NEVER considering editorial clients for representation, or vice-versa, I would avoid. Just . . . make sure.
3) Agents who have some other miscellaneous side-job: Most agents, when they start out, unless they married rich, have another job in addition to working on their client list. Very often, this job is being a full-time paid assistant or secretary at the agency, and being given the opportunity to take on a very few clients as well -- but these clients must be dealt with AFTER all the other stuff is dealt with. Sometimes they have a job outside the agency.
My own story:
I am an agent at one of the biggest agencies in the country, with 150+ books sold on behalf of my clients. I worked full time as the buyer for a bookstore when I started as an associate agent. I don't think it affected my clients in a negative way at all, and I sold lots and lots of books to publishers while working two full-time jobs.
Since I was promoted to a full agent, I pulled back significantly on the bookstore, for time considerations - but I will always work in a bookstore. Always. I don't do it for the money - I do it because I like it, and I want to, and quite frankly, it's none of anybody's business WHAT I do with my spare time as long as it isn't affecting the job I do for clients. I don't complain when somebody has KIDS for pete's sake, and god knows they take up a hell of a lot more time and energy than a few hours in a bookstore! Jeesh.
Also: I'd really like to know where they get that 2 months of lovely vacation, because it isn't America, that's for sure.