As a point of interest.
Another server I have played on handled expanded summons quite well I think.
There were a number of Summoning Books available as loot drops, covering Animals, Elementals, Undead, Tana'ri, Baatezu and Celestials.
Using a book opened a conversation, in which the user selected the spell to alter (Summon Creature I-IX, Create Undead, Planar Binding, Gate). Each spell had only one alternate option, flavoured by the theme of the book. The books could be used indefinitely.
As a example, Gate could be changed to summon a Pit Fiend, Balor, Solar, Ancient Elemental or Demilich.
This opened up a great deal of RP potential as the Summon could be tailored to fit a particular scene/event. In terms of dungeoning only the same few were used consistently (those with buffable weapons / DR).
Another method I have seen is 'Summon Tokens'. These are single-use consumables which change a specific summon spell to a specific creature, I think permanently. If you wanted to change summon, you have to find and use another Summon Token.
Obviously all those choices took up palette space, but I do think the Summon Tome was an elegant solution to a distinct lack of choice in vanilla NWN.
I would not advocate such an extensive array of choice, as summons are meant to be restricted in Ravenloft, but you could, say, make available 3-4 Tomes which offer a selection of Ravenloft-friendly creatures to summon, like Dread Treants, Mist Horrors, Wraiths, Fire Minions etc.