I don't think they are related. On deviantart, there is a very talented artist, and she made a family tree with all canon and subcanon characters. Tojo and Simba aren't related there. Also, Tojo is from a neighbouring pride, which means they cannot be family. Since prides are lead by males, and they kinda kill of cubs that aren't their own in nature. I think the similarity between Tojo and Simba is the result of lazyness of his dezigners
missing the old deviantart...