I think the question here is picking the lesser of two evils. With the disk configuration you have I think you have two choices.
1) Install MSDTC and SQL into the same Cluster resource group on the same disk resource
2) Install MSDTC and the Quorum onto the same resource group on the same disk resource
Personally, I'd go with option 2 and found the following snippet on blogs.msdn
Should MSDTC be in its own resource group?
To help ensure availability between multiple clustered applications, Microsoft highly recommends that the MS DTC have its own resource group and resources. If MS DTC cannot be configured to have its own resource group, the recommended alternate choice is to use the Cluster group and Quorum drive.
Hope that helps
Adam