No, each SQL instance needs to have it's own drives and it's own drive
letters.

Denny

In an MSCS cluster, a resource group is a unit of failover. If two groups
were allowed to share a disk, that disk would be a resource in both groups.
When you failover one group, that disk resource is failed over, and because
that resource is also in the other group, the group much be failed over all
well, which defeats the whole notion of a resource group being a unit of
failover.

Linchi