Is a direct or import approach safer for migration into WordPress?

If this is a standard CMS (not something you came up with yourself), I would say that a WXR solution is the way to go. It might take some extra work, but it will be a good learning experience and a nice way to build up your WordPress skills. The WXR route will be an automated solution that’s reliable and repeatable.

You might want to consider doing this as an open source project, soliciting help from the community to get it done. The end result will be a useful tool from which others can utilize, improve, and extend. Open source contributions are always nice to list on the resume, too.