That’s the theory advanced in this NY Times article. If true, it would certainly be something to worry about. But I would like to see some hard evidence of this effect at work. You could imagine, for example, that concerns about voter suppression and disenfranchisement could actually serve to increase turnout as a way of countering that effect (indeed, stories such as this could be used to have that effect).
To test this question, I suppose one would have to do a post-election survey of African-Americans who voted and who did not, asking those who did not vote the reason or reasons they chose to stay at home. My guess is that few would actually mention the possibility of the election being “stolen” or voter suppression.