Hello and welcome!
I'll start by suggesting that the guidance you have been following was not sourced from the OpenBSD Project, as some of it is incorrect.
- The "In /etc/rc.conf ..." guidance is incorrect in two ways.
1. Do not edit the /etc/rc.conf file. You must have missed the comments at the top of the file explaining that it should not be edited, and instead, local provisioning should be made in the file /etc/rc.conf.local.
2. The "dbus_daemon" has not existed by that name for more than two years.
- Gnome must be started from GDM, not from startx, unless you have special requirements, and it is not recommended as a) you do not have complete Gnome session management, and b) it requires careful, special provisioning.
The guidance you SHOULD follow instead of the guidance you have been using is the gnome package "README", which was installed in /usr/local/share/doc/pkg-readmes when you installed Gnome. A message telling you that documentation was installed there appeared on your console, but you must have missed it.
The yelp application (Gnome's "help" browser) is not available on Sparc64.