Yes the station is listed on Page 2 of the WTT but nowhere else. Strange because even places where trains don't stop are listed in the timetable section, such as Neasden and Watford South Junction. Do trains to/from Watford actually stop at Croxley? Not something I can check out since I am located on the wrong side of the pond.
The Working Timetable is for the operating department, not the passengers. Only specific critical timing points are listed in the main pages, such as terminals, crew relieving points, junctions. Individual stations are not always important for the operation of a railway.
Unless Croxley were to be temporarily closed for some reason all trains on the Watford branch call there. There are several other stations not shown on the actual timetable pages; Ickenham, Ruislip Manor, Eastcote, Great Portland Street, Euston Square, Barbican. Conversely, passing times for Neasden are shown but Met line trains don't call there in passenger service. Perhaps a Met Railway hangover in the timetable?
Edit: Posted before I noticed Dstock7080 had already covered the point.
Yes, Watford trains stop at Croxley. They'd have to - Croxley only gets trains going to and from Watford, otherwise Croxley would get no service.
Is this the document you are referencing? As Harsig points out, it seems WTTs do not list all stations (for example, this one does not have Euston Square, Great Portland Street, West Harrow, Eastcote, Ruislip Gardens, or Ickenham, and the Bakerloo one skips many stations as well). I don't know much about time tables, but I can guess that Neasden is shown as it is a depot used by Metropolitan Line trains, and that the junction is used to aid with scheduling trains or to use as a defined checkpoint for train times - I'm not entirely sure.
Edit: Well that makes two of us - This was also posted before I had checked to notice Dstock7080 and t697 were much quicker in writing a response. Perhaps it's the more the merrier, or have too many cooks spoiled the broth?
Neasden (station) may be in the Met WTT more for operating staff benefit. I wonder whether unofficial 'taxi' service will have to stop when that area goes ATO.
I imagine it will be the same prinicple as the staff hault on the jubilee line between West Ham and Stratford IIRC if you require "picking up" you press a button on the hault or contact the LC who will arange a train to travel in PM and stop at the hault to pick staff up.