^But if every series had only one writer, then there'd only be a half-dozen or so people writing Trek novels on a regular basis, depending on how many book-original series there were.
I had a feeling that there aren't much more than half a dozen regulars either way, so I've gone through the schedules from 2011 to 2014 (as far as we know if ATM), and if I haven't miscounted there are eight authors/writing duos who have three or more novels during that time frame (I would say less than that shouldn't count as regular). So I guess there are a couple more "regulars" than I thought.
9 novels: David Mack
7 novels: Dayton Ward (3 with Kevin Dilmore)
6 novels: David R. George III
4 novels: Christopher L. Bennett
3 novels: Michael A. Martin, Kirsten Beyer, Greg Cox, Una McCormack
2 novels: James Swallow, Jeff Mariotte
1 novel: David McIntee, Peter David (published twice), Marco Palmieri, Steve Mollmann & Michael Schuster, Tony Daniel, Alan Dean Foster, William Leisner, Jeffrey Lang
By the way, that KRAD isn't even on this list with a single novel is a fucking shame.