The difference in power between the Vortex and the Vectors will vary, depending on tire pressure, how hard the roller presses against the tire and temperature. If you like, you can fiddle with the roller tension to get them to align pretty well.
One reason using Power Match could be a good idea, is temperature drift. As the trainer warms up, the displayed watts can change by up to 20 watts in a normal room temperature. If you work out in a colder room, it can be even more. Last winter, I did a 2 x 8 min FTP test in my cold shed (around freezing) and it gave me a FTP of 316. Looking at other ride data, my FTP at the time was around 250, maybe closing in on 260, but certainly not anywhere near 316!