If you want the scheduler to load a playlist, it needs to be a program playlist, not a spot playlist. If you put those files into a Radiologik program, and save choose "Save Program As", naming it appropriately, the scheduler will be able to add those in.
As far as not having them not overlap, there are various ways to deal with that. You can put short silence tracks between them. Perhaps necessary at the start of several to compensate for the overlap of the previous song. You can edit the properties of the files so the fades are zero, and the overlap is 0, and not default. By setting a 0 for overlap, it overrides the overlap value in the preferences. I don't actually have a large overlap value in the Radiologik preferences, so nothing really overlaps by default. I rely on the track properties to overlap songs. Because an ad won't have an overlap value, they don't overlap anyway.
Personally, I do advertising a little differently. I'm making use of itunes playlists and smart playlists to select ads to run. In my case, I'm mostly random with ads, and mostly only control what time of the day they are allowed to run. So I have codes in the grouping tag like "morning", "afternoon" etc. A smart playlist for morning ads will only have ads that have the 'morning' data in it's grouping tag.
There are lots of ways to do this kind of thing, depending mainly on your own personal requirements.