Let's look at the definition in the SDK Reference for both:
VM - Amount of actively used virtual CPU, as a percentage of total available CPU. This is the host's view of the CPU usage, not the guest operating system view. It is the average CPU utilization over all available virtual CPUs in the virtual machine. For example, if a virtual machine with one virtual CPU is running on a host that has four physical CPUs and the CPU usage is 100%, the virtual machine is using one physical CPU completely.
Memory usage as percentage of total configured or available memory, expressed as a hundredth of a percent (1 = 0.01%). A value between 0 and 10,000.
- Virtual machine: Percentage of configured virtual machine “physical” memory:
active÷ virtual machine configured size
Note that the definition places "physical" between quotes, it's what that VM thinks is its physical memeory. And the value is a percentage, if you allocate let's say 2 GB to a VM and the VM's active memory is 1GB, you will see 50% in this counter.
To answer your question, yes it is virtual CPU and memory that is expressed in these counters.
Btw, you can combine multiple counters in 1 call to Get-Stat. It will be faster than 3 separate calls.
$counters = "cpu.usage.average","mem.usage.average","net.usage.average"
Get-Stat -Entity $VMName -Stat $counters -Start $day1 -Finish $day2