Do I need a seperate XML editor to edit FrameMaker DITA generated files?

The thing is, DITA doesn't fit for everybody. To have a successful DITA workflow, you'll need full approval of your authors. If they don't like DITA and don't support it, you are going to end up with lots of costs while building the workflow and even more costs cleaning up the mess they caused after you change to some other structure.

DITA is still foremost very good at one thing: software documentation. If you do anything else, you will most likely end up using some other XML environment (yes, I know DITA specialisations and DITA 1.2 change that a bit, but still).

The best you can do, is to sit down and try to figure out what structure fits best to your documentation needs. Analyse your documents and see, if DITA fits to it. Estimate how much work a specialization would be. If there's too many changes you would need to make, you're most likely better off using a custom structure.

You need to check all angles of implementing a structure, from building up knowledge, training your writers, writing and _maintaining_ the structure and adaptions, acceptance by your writers and so on.

If after all evaluation still DITA stands on your paper, go for it. If something else is written down there, go for that.

Our company ventured too into the wilds of DITA, but we had to leave those wilds for good to keep in business. And I'm still trying to clean up the mess, that venture caused.

tldr;

I'm not voting against DITA here. What I'm voting for, is a well planned move towards structured authoring. Don't get hasty, don't run after the fancy car they're trying to sell you, keep a rational view on things and especially keep your eye on the acceptance of your writers.

There's nothing more messy, than to clean up after a half-assed try to implement something unsuitable or unwanted.