The "readme" for Patch 9369783 (which covers the AprilCPU for our 126.96.36.199 HPUX-IA64 environment) includes this short reference to DataGuard:
If you are using a Data Guard Physical Standby database, you must first install this patch on the primary database before installing the patch on the physical standby database. It is not supported to install this patch on the physical standby database before installing the patch on the primary database. For more information, see My Oracle Support Note 278641.1.
When checking that note 278641.1 we see that it also appears to only cover 10.2. Although this note has more detail, it is clearly the same procedure as discussed in 813445.1. Therefore, the conclusion that I make is: OPatch works exactly the same with DataGuard in 11g as it did in 10g.
We will be upgrading our DataGuard enviornment to 11g in one-month. At this point, I am completely expecting our OPatch procedures to remain unchanged from what we have done for years with 9i and 10g. I would also note that the upgrade procedures we have tested (involving DG from 10.2.0.4 to 188.8.131.52) are nearly identical to the above mentioned support notes.