yes, but you will also, need to apply the group based permissions to any sub-forums under the main 'group forum'

ie: even though you might logically group a forum and it's sub-forums together as one.. you will still need to group each child forum as well..

i do this all the time..

like

'uber geek forum' -- geek group main forum
'uber geek games sub forum' -- geek group sub forum
'uber geek whatever sub forum' -- geek group sub forum

'special peeps forum' -- special group main
'special peeps sub forum' -- special group sub

Enjoy,
SD