好像是的，我之前也碰到过，11.2.0.4及之后都可以。

Mos相关bug，你可以看看

Bug 11715084 - Active duplicate should work when connected to Standby as source DB (Doc ID 11715084.8)

Bug 14263190 - A duplicate fails with RMAN-5531 when source is a standby (Doc ID 14263190.8)