Some generic info about Nezumi as pertains to Drakara:
The Nezumi are from a civilized culture located in/around the great swamp across the southern part of the Drakaran Sea to the east. They are renowned for their cunning and fleetness of foot, and their favored class is thought to be Rogue, by those who think about such things... Most Nezumi within the Drakaran Empire are merchants and diplomats. PCs would know that the Nezumi live in the Great Swamp across the Drakaran Sea, and have some vague idea of the general tendency of Nezumi to have stealth-related skills, as well as tending to be somewhat abrupt in their manners. (Too hasty! In more of a hurry than most humans! => -2 CHA - and it is known that Nezumi grow up quickly and age quickly as well.) If anything, they may be considered a bit chaotic simply because the Drakaran general outlook is so pro-status-quo...while the Nezumi may be slightly innovative. Oh, and sometimes they bite...
[As far as player knowledge goes, the description in the O.A. book is fairly good as far as abilities and such, but the cultural info is off a bit -- although they may have a very slight tendency towards chaotic alignments, they are not actually nomadic types living in a wasteland (i.e. there is no Shadowlands region), they do indeed live in cities as well as villages, though a few are somewhat nomadic swamp dwellers too. There are some minor adjustments -- their immunity to the Taint translates to (a) the ability to handle Obsidian with no chance of being cursed and (b) some innate resistance to Evil magics. (They have a +2 to save vs Evil magic.)]
The Nezumi do have some 'nobles', i.e. Aristocrat class applies, but not Samurai or Shugenja -- as well as some 'wild ones', i.e. Barbarian class applies (and a Nezumi barbarian does indeed have a speed of 50') as well, with Aristocrat or Barbarian being taken at 1st level or not at all. The bulk of Nezumi are the equivalent of Common Drakarans, with seven of the eight common classes being available (no Wu Jen). The Nezumi have clans or families, sort of, but not in a way that the Great Clans of Drakara truly understand (nor do they choose to try), and they are not allied with any specific Great Clans. Some of the Great Clans may find it easier than others to get along with them - most notably those with a little more flexibility of attitude such as the Scorpion Clan, or those for whom fighting the denizens of the Wilderness takes precedence over other considerations, like the Crab Clan, or those who are oft considered 'outsiders' to some extent themselves, like the Unicorn Clan. But no Great Clan has a really close working relationship with the Nezumi, other than in mercantile matters, which are usually handled by underlings rather than the heads of the Families in any case. (The Dragon Clan has the most contact with Nezumi in terms of trade outside of Drakara City.) There is apparently no Nezumi Emperor, indeed it has never been exactly clear to Drakarans just what the Nezumi political structure is like, but it does appear that individual Nezumi ambassadors are able to speak for their people as a whole, at least in matters of trade.
Most common Drakarans have only a vague understanding of Nezumi, or 'ratlings', often confusing them with goblin rats and/or rat hengeyokai, but those who have lived or spent much time in Drakara City would have more understanding of them, as the bulk of Nezumi in the Empire live there, acting in both diplomatic and mercantile capacities - a few may be found in other ports up and down the coast of the Empire, but they become much more rare as those ports get further and further away from their homeland. Nezumi have their own ships as well, and many are accomplished sailors, their natural agility and speed serving them well on the open seas. At the Imperial Court, the few Nezumi ambassadors tend to be fairly quiet and observant, keeping a low profile. In Drakara, even amongst those used to them, most Nezumi wear somewhat concealing garments so as to not frighten the servants and other common humans unduly...
Nezumi do not study magic in the way of the Wu Jen, but DO have Sorcerers, and indeed, Nezumi Sorcerers develop a slightly different set of potential spells, in that they use the Wizard/Sorcerer list from the PHB instead of the Wu Jen list from O.A.! Nezumi Shamans however are per standard O.A. domains and spells. [PCs would have only a vague idea that some Nezumi magics are 'strange' but that their shamans have the same reverence for the spirits as Drakaran shamans.] Other common classes fulfill much the same roles in Nezumi society as they do in Drakaran society, though perhaps with their own peculiar slant on things.
And that is about it, as various people pool their knowledge (or lack thereof) about the Nezumi...