No is my understanding.
You can perform a Rolling Upgrade :
See "12.6 Performing a Rolling Upgrade With an Existing Physical Standby Database" of Oracle doc E10700-02
Step 8 Perform a switchover states "Both databases must be running the higher version of the Oracle software".
The documentation says the compatible parameter needs to be the same between primary and physical standby database.... so, they can run at different patchset levels, but must have compatible set the same.