Marc,
I have customers who have asked to have this configuration implemented with MPxIO. I have not personally tried this with mpathd however. DMP will work with native volume managers and TPD multipath utilities (powerpath for example), however to use VxVM with mpathd would most likely require suppressing the devices VxDMP's view using the command "vxdmpadm exclude all"
https://sort.symantec.com/public/documents/sfha/5.1sp1pr2/linux/productguides/pdf/vxvm_admin_51sp1pr2_lin.pdf
Take a look at pages 184-185.
This however would not be a recommended configuration as DMP will provide substantially more array based information and I/O path options with its sub-path failover functionality. Essentially DMP is able to not only identify a failed path but it can quickly determine any and all subsequent paths that would all be effected the same failure. Therefore it need not test I/O down those paths. Imagine a system with 2 HBA ports x 2 Switches by 8 Array controllers ports (A/A or A/P). You could have upwards of 16 paths to a device. If a single switch fails, native multipath drives will check all 8 paths associated with that switch. Whereas DMP acknowledges a sub-path which would allow for a seamless transition to an active path with testing additional failed links.
Hope this helps,
Joe D