Running an I/O on "earmuffs"

[Hillcountry]

I have hooked a hose up to my Volvo Penta to start the motor in my driveway to check things out and don't have a problem doing so but my question is, is it okay to put the motor in gear while on the muffs?
i have been showing the boat to prospective buyers and not starting it but would demonstrate how good the motor runs by using the hose and muffs...just wondering if it's okay to put it in gear to mak the prop turn (carefully, of course)