MMM 2.x uses log4perl for logging. You can create a custom configuration file[1] for log4perl and use the perl module Log::Dispatch::Syslog (don't forget to check whether it's installed on your hosts) to write log messages to syslog.
I think Section 4 ("Logging messages to Syslog") on [2] will help.
Cheers
Pascal
[1] http://mysql-mmm.org/mysql-mmm.html#SEC60
[2] http://netlinxinc.com/netlinx-blog/52-perl/126-eight-loglog4perl-recipes.html