cvs-update-prog-output-skip-regexp is a variable defined in `pcvs-parse.el'.
Its value is

A regexp that matches the end of the output from all cvs update programs.
That is, output from any programs that are run by CVS (by the flag -u
in the `modules' file - see cvs(5)) when `cvs update' is performed should
terminate with a line that this regexp matches. It is enough that
some part of the line is matched.

The default (a single $) fits programs without output.

You can customize this variable.