Zenoss uses the standard Python “logging” module for this. The levels are a bit counter-intuitive in that a lower numbers gives your more verbose logging.
50 = FATAL/CRITICAL 40 = ERROR 30 = WARNING 20 = INFO 10 = DEBUG
So setting logseverity to 10 in zenactions.conf (or any .conf file), or via the command line with the –logseverity option will give you all possible logging. The default is 20 or INFO.