The only things that are important are that the gauge be correct, the rails be the right size, and the clearance between the rail and the track-tie be sufficient. Beyond that, it doesn't matter what shape the track ties are, what they are made of, what kind of backbone the track has (or even if it has a backbone) or anything else. Basically, so long as they maintain sufficient clearance for the wheelsets and use the same size pipe, the difference between track types is a non-issue.
--Dave Althoff, Jr.