
i would do it that way:
use the gamut node or the OCIOColorSpace node to bring all your footage into the ACES colorspace then comp as usual (i guess this would work because ACES use a linear gamma but with a bigger gamut and fusions internal math is expecting linear images)
then use a viewer LUT as normal and depending on you needs
before the output/saver put another OCIOColorspace node and transfer into your delivery space
*edit*
because fusion uses hardcoded Rec709 Primary chromaticities in some tools (saturation in CC and BC) you will not work in ACES gamut correctly