No I was not saying that a digital ballast not good for a closet room,

What I am saying is the actuall ballast has to be placed in a cool place with good air flow. You can put it in your grow space if you have good ventalation and the temperature never goes above 80f. Also the ballast has a cooling fan and if there is any restriction in air flow it may overheat the ballast. I also don't recommend setting it on the floor exspecially carpet. Carpet is an insulator and will cause heat buildup.
The way I have mine is hanging from a screw on the side of my cabinet with 1" air space between the ballast and cabinet so air is flowing freely on all 4 sides.

As for attic growing I do not recommend using a digital ballast for this due to the extream temperature fluctuations. I don't even recommend growing up there at all.