I am just under 14 years late to this, but I will finsih running my Red Hand of Doom campaign for 5e and we will be going into RtToH afterwards.  I have always wondered about this connection.  Thank you!  
Here's a thought - what would Hades make of Acererak / Lichdom / Orcus?  I can't recall running into Hades as a deity / power in DnD aside from Deitieis and Demigods, but he has an outer plane in his name....  
Take care all,
Ross