Simon,
This is definitely possible and recommended for true production environments. If you're just looking at changing the glogowner password, then you'll just need to update the glog.properties file (on all tiers) and remember the password for applying OTM patches (i.e. running the dbpatch_55.sql script).
If you want to change other usernames/passwords, then the list expands beyond that. I believe the the following is a complete list of OTM DB users:
- glogowner
- glogdba
- glogdev
- glogload
- archive
- build
- reportowner
Hope this helps!
--Chris