That is a good question. We have a EMC 3830 running Timefinder BCV's.
All a BCV is, is another mirror copy. A "Second mirror". Note however, that an EMC box does not do physical disk-to-disk mirroring. A physical will be broken into many strips, with each strip being either a primary, a mirror or a BCV.
In our configuration, the primary is mirrored, the BCV is mirrored, and BCV's are configured via the BIN file to connect to another host. We perform a split, and in 2 minutes we have a point-in-time copy - on a different server.
In order for your scenario to be true, you would need to have the BCV's and primary's on the same host. In addition to that, they would need to be active on the same system at the same time, which would be difficult to manage - if you were to write to the primary and the BCV at the same time, you could get corrupted data.
So I guess I'd say - in answer to your question -
No.
Bill.