The Disk Utilization rule detects volumes that cause performance bottlenecks. Bottlenecks occur when a disk is highly utilized and performs a high rate of read and write transactions.
The File System Capacity evaluates free space.
For Windows the "Disk Utilization" rule is scoped on physical disks using Win32_PerfRawData_PerfDisk_PhysicalDisk while the "File System Capacity" rule is scoped on logical disks using Win32_PerfRawData_PerfDisk_LogicalDisk.
The "Disk Utilization" rule works on physical disk and it will not provide a disk name in the alarm message as it is not common to have a disk name for a physical disk.