i do think its better to have genuine black people but only for authenticity.
it is always better to have the real thing.
but i dont think there is anything wrong with blacking up - the whole of theatre and tv and film is about 'faking things' - about changing the way actors look to suit a role.
people put on weight, lose it, are aged, are made to look ill, or injured, have hair shaved or changed etc. some make fake chinese/japanese eye parts.
if they were blacking up to take on a stupid cliched minstrel type part, a figure of ridicule, then yes its innappropriate (unless thats what the film is about)
its different in films as theres no need to do it, there are plenty of actors, but in small budget local theatres they often have no other option - as happened in this one.
it would absolutely not be racist to say that in the ad either - all ads for actors are very specific ... they have to fit the character - and will say things like, must be fat, skinny, dowdy, tall, young old etc etc.
it is not like a job in a bank or something.