There was a similar discussion post at this thread. From some internal information I can see that this may be similar to a Hilbert Transform, but that doesn't mean to say it definitely is a Hilbert Transform. This particular VI was developed a while back and it seems as though the developer has now left NI, so I am afraid we cannot give an exact answer.
My suggestion would be, if you are unsure and require a specific technique, to create your own Envelope Detection VI. Otherwise, if the technique is not that important and you just need to do Envelope Detection, this VI will work fine.
Thanks for the reply. If I try to open the thread it gives me an error that I do not have access to view this page. But it was more than helpful to know it is similar to Hilbert transform