In what way?
What did they bring that made the game or game world better?
Not as an argument, I just don't remember those. Not just by name at least.
Well, Raven is probably a bit of a false inclusion - I just like her. Geoffrey is funny and the only character I can think of off the top of my head who represents evil magical snobbish Victorian aristocrat well. Madame Lil I loved for the running of quests for the owner of a brothel; I just can't remember ever getting to play sleazy errand-boy/problem solver in a game before.
Lianna Del Par I always remember; she provides a ton of information and flavor to Cumbria. Plus she just seems badass; pretty much anyone who ever played a thiefish character in Arcanum spends most of the start of the game robbing everyone in the first city and/or Dernholm, checks out that sword she's got, tries to pickpocket it, inevitably fails, and then watches as she annihilates you in like two swings.
And Cedric Appleby is entirely optional as far as ever interacting with him, but he just makes so much sense as the jealous slightly deranged rival of Bates.
I guess I just think a lot of the side characters in Arcanum are realistic and written really well - from the guy who wants proof that his flying machines worked, to the mob bosses in the Boil, etc. They're not just there to be fonts of XP, you really feel like they're somewhat real, with normal people motivations. I always feel bad for Liam's mother when I have to come back and tell her that her son got ganked by a bunch of lizard creatures - even though that's pretty much the only interaction with her in the whole game.