I think the reason behind the lack of Olrox art is because he isn't one of the important/main characters in SotN. He was just another boss whom by now has gathered a larger then intended following.
Hmmm. Maybe the best way to actually solve that problem about Olrox being place at the back cover box is to let someone who is actually willing to draw Olrox once again with high-quality and full image picture of him. Don't you think? Ahaha. On a side note X, in Castlevania: Souls of Sorrow storyline, Olrox is a character which portray as a revengeful person upon his elder brother's death. If Brauner would ever return in Souls of Sorrow, Olrox won't ever seeks his revenge. You see now?
. He is an immortal vampire and a high-class vampire. Sometimes, he screaming like a mad man as if nobody else on earth. However, he doesn't even respect Lord Dracula nor anyone who surpass him before. Even his appreciation over Death for reviving him, none at all. Cold, hatred upon the humans and enjoy killing anyone who stands in his way, just like his elder brother. Legendary son of Lord Dracula, Alucard, may have defeated him once but the man, who can bring back alive from the dead, Death, resurrected him by using Olrox's SOUL. Death tells Olrox everything about what had happened to his elder brother, Brauner. One of the scene in the game, he quoted "I, am Olrox. I seek revenge upon MY BROTHER'S DEMISE! HEAR ME DEATH! I DO NEED YOUR HELP DEATH! I WANT TO BE STRONGER THAN ANYBODY ELSE IN THIS WORLD! NOR IN THE NETHERWORLD! I, SHALL BE THE NEXT DARK LORD! *Evil Laugh*" Death response in a mysterious and wicked way: "Hehehehe. Whatever words you may say my dear Olrox, you shall seek your vengeance. Soon, soon enough. *Evil laugh*"
Another reason why Jonathan and Charlotte becoming old simply because they are just a merely human beings who has the ability to actually holds the ultimate vampire killer whip and a holy book due to their forefathers generation. So the time machine basically couldn't reach into the time where Jonathan and Charlotte were once at younger age. Another reason why Death brings Old Jonathan Morris and Old Charlotte Aulin back to alive from the dead is simply because Death wants Olrox to live in an agony, rage, revengeful and more hatred towards the humans and especially to the one who killed his elder brother. But in fact, as i mention earlier, Death was the one who killed Brauner. Olrox doesn't even know about the truth. The reason why Death wants Olrox back to alive simply because Death is actually...I can't tell you right now, i don't want any spoilers until the end of the chapters. You'll know soon enough, don't worry. Hehehe
I know you can't wait to know about it.