To add some info to this for all it is worth: after a lot of testing i was not able to get the above to work, even though the command function in
Blue Iris was actually working well with other executables.
Then I stumbled across this utility with a similar name :
bp2008/MonitorControl
This one works via http requests, so you would use that instead of running a program locally. It also works remotely so it can wake up other computers than that where Blue Iris is running on. It also has some additional parameters to switch the monitor back off after a set time, or according to idle conditions. I got good results when for each of my cameras I first send a "Cancel" command and then a wake up + sleep after x seconds. I removed completely the Windows power settings on switching off the monitor as this one gives better control.