Ach! I forgot about Frondo. Can't say about R'yn Diak, but I would say that the Jaheira reference could well be legitimate, considering the dev mindset, but I agree that it's a bit of a stretch. As for the anagram, I doubt it just as much as you do. It wouldn't have been hard to name him R'yn Diaak or Rayn Di'ak or R'in Diyaak or something, and it would have made more sense. Still possible, especially considering the thought that it could have been a play on the name, but I doubt it.
Also, Herkemer Oggdoddler, a bitter Cumbrian ex-soldier (and melee, dodge, and firearms expert) living in Blackroot, may be a reference to Brigadier General Nicholas Herkimer (1728–77), who was the commander of American forces at the Battle of Oriskany in 1777, was wounded therein and later died as a result of his wounds. Oggdoddler's descriptions of the last great battle between Cumbria and Tarant reflect General Herkimer's decisions, failures, and ultimate regrets both during and after the battle. I don't remember very well, so don't quote me, but Oggdoddler may also have claimed to have suffered a severe leg wound during the battle as did General Herkimer. Details of the actual battle are available all over, but I found one particularly relevant account here:
This WAS an edit, although I don't see anything indicating that below the post. Maybe it's just me.---->EDIT: One more. The rather comical pamphlet given to you by the priest in the Panarii Temple in Tarant's commercial district contains a clean, pure, easter egg. Part of the pamphlet reads: "'I've never been happier! I've even sold my Staff of Hideous Death!' -Wermian Doone, Former Dark Necromancer." This is a reference to a premade character, Solomon Doone, whose short biography denotes his birth unto a long line of evil necromancers. Again, I apologize for posting so liberally.
Also, I just remembered a reference, (I BELIEVE in one of those random pub sequences in which you wager 500 coin on a sometimes very easy, sometimes very obscure question.) alluding to "Cumbrian fire" being used as a last resort during the war with Tarant, a reference to the somewhat well-known "Greek fire" made use of minimally by certain Greek city-states, and more famously by the Byzantines, or Eastern Romans in limited naval warfare.
Dear lord... ALSO: The F1-F6 hotkeys which host follower commands have their own easter egg, another I had forgotten, (and possibly one of many) that being found in the jocular spurts of random dialogue which occer if you should attempt to use one of these commands while out of fatigue. "#Troika" can randomly appear while doing so, this as opposed to "#fjsapi" or "#urgvsk" (or whatever they might actually be) as substituting for "#Attack" after taking one too many Orcish maces to the face. I'm thinking of loading up the game for old times' sake to see if there are any more, but have been busy. I haven't the intimate knowledge of Arcanum's source code enough to, say, scroll through the possible outcomes of mashing commands during knockoutedness, and lack the inclination to do anything to that end beyond whining about it.