I did more tests, here's the result:
for standard version:
1.lsws native vhost's access log format is customizable
2. if vhost is read from apache's httpd.conf, log format is fixed(bug ? or for performance ?)
you can create 2nd log, but format is "combined", cutomized LogFormat is ignored. the 2nd log file is created there.
3. for enterprise edition, LogFormat from httpd.conf is working as expected.