Is it just me or is 'Bombus lucorum agg' not in the drop down?
It does not appear to be at present. Use "Bombus lucorum sensu lato" or "Bombus lucorum/magnus/cryptarum" as the species on the record.
Is it a useful addition to the species dictionary?
It might help some recorders getting their record into the system but as it would be an "agg." and not a species level ID records would get verified as "Plausible" and go no further as far as BWARS is concerned.