Oracle Data Guard and Active Data Guard are basically GUIs used to accomplish some form of data replication. I have been doing data replication with Oracle since 1990 where I built a rapid prototype, integrated, distributed database system between Fort Lee (Oracle/PC) and Fort Monroe (SQL DS/4381).
Designed, coded, and demonstrated product in four weeks.
Since 2008 I have built and maintained several log-shipping instances in Standard Edition. In addition to running one failover site, we also ran a disaster recovery built the same way. The failover was a manual operation and took about 15 minutes to complete with less than two minutes of customer down time. It worked identically to either site: failover or DR.
Standard Edition does not come with Data Guard. Oracle SE licenses are much less expensive.
Additionally, I have implemented true Master/Master replication for five, six and eighteen nodes.
While I do not have Data Guard experience, I have no qualm in using it in some future endeavor.