I wouldn't recommend that you span a partition over two virtual disks, the reason being is if there is a failure of one of the VDs it would affect the partition, and also by doing so you increase the chances of it happening as well.         
I have an MD1420 connected to an R740 running Windows 2016 server. The C drive is on 2 mirrored drives on the server. I have 2 data drives - one on the internal R740 disks (S drive) and one on the MD (G Drive). I have 4 TB of disk space free on the 740 internal disks that I'd like to use to extend the G drive, but Windows does not see them as contiguous. Is there an easy and safe way for me to change that so I can add the space to G? If not, I can create another drive with the free space, but extending G would be my preference. Thanks.
Merging disk allocation on R740/MD1420