I see no obvious objection to your scenario _assuming_ a 'niche' exists such that said organisms might receive appropriate levels of ionizing EMR to meet the requirements of "photo”synthetic functions while maintaining sufficiently low temperatures... --- A ‘neat trick’ in consideration of the fact that, while ('pressure issues' aside) your model is readily amenable to adjustment of ambient temperature via ‘altitude selection’, the dielectric constants of organic compounds are such that hertzian & (especially) IR heating will be a principal factor - aggravated to no small extent by the 'fragility' of such compounds (CIP) liability to pyrolysis at relatively low temps)...

All this aside, I *do* feel your scenario has merit! :-) -- Perhaps ‘bio-terraforming’ will find its way into the lexicon in the not so distant future :-)

Just my $0.02

Best regards
Dan Sarandon