Merchants and nomads, as foretold (although it did turn out that my BR numbers were high because I gave them the extra attack for being veterans, which they don't get because they're cavalry. So it's good that I took the time to check, though I'm still not highly-confident in these BR numbers).
The sort of NPCs that more scrupulous players might consider hiring. Or use the caravan guard stats for when PC-backed brigands are raiding.
Men, Merchant Caravan Guards: 2/3/4 Loose Foot, AC 4, HD 1, UHP 8, ML +1, 3 sword and dagger 9+ or 3 crossbow 10+. Every 10 wagons is guarded by 2/3 of a platoon (5/8 UHP on platoon scale). Might be allowed to deploy as Formed Foot with 1H sword used in both hands, but it's sort of weird for them to use crossbows then.
The stats of the 5 merchants per 10 wagons are unclear. I guess the Men monster entry does say that everyone in it fights as first level fighters. They do have chainmail, daggers, and crossbows, which also suggests that they fight. A mixed unit of caravan guards and the merchants themselves (dismounted) probably has 6 or 7 UHP instead of 5 on platoon scale, but otherwise fights about the same.
Basically veteran crossbowmen with two-weapon fighting.
Company BR 5.25, individual BR 0.044, individual wage 33 gp/mo.
The 5th level guard captain is each caravan is qualified to serve as a commander at platoon scale, which is perfect.
Men, Nomad Archers: 4/8/12 Irregular Mounted, AC 3, HD 1, UHP 8, ML 0, 2 short sword 10+ (plus 3 hooves 9+ on charge) or 2 composite bow 10+. It's odd that these guys are mounted on riding horses instead of warhorses, but that's why they're irregular. A caravan of nomads is about two platoons. Company BR 2.5, individual BR 0.023, individual wages 18 gp/mo.
If mounted on light warhorses, Nomad Archers may be Loose Mounted, losing the hoof attacks on charge but gaining the ability to withdraw. Loose Mounted Nomad Archers have a company BR of 8, individual BR of 0.066, and individual wages of 50 gp/mo (which seems reasonable - a horse archer is 45gp/mo with better morale but fewer HP and worse melee)
Men, Nomad Lancers: 4/8/12 Formed Mounted, AC 3, HD 1, UHP 8, ML 0, 2 lance 10+ or 2 short sword 10+ (plus 3 hooves 9+ on charge). A caravan of nomads is about two platoons. Company BR 4, individual BR 0.033, individual wages 24 gp/mo. If Irregular Mounted, company BR 2.5, individual BR 0.021, individual wage 15 gp/mo.
Main difference between nomad lancers and veteran light cavalry C is the nomads' much weaker morale. If I increase their morale to +2 I only get company BR of 4.5 and individual wage of 27 gp/mo, versus veteran light cav's wage of 42 gp/mo, so I'm not sure if I'm hitting an edge case or there's a bug in my BR calculator or if it's because my "number of melee attacks" input is already rounded instead of unrounded or what.
The 4th level leader of each nomad caravan (wilderness encounter) is not qualified to serve as a commander on platoon scale (but he only has two platoons so fighting it at squad scale might make more sense). The 8th level chieftain in charge of each lair is definitely qualified to command at platoon or company scale, and gets about 14 platoons of cavalry in expectation (with possibly as many as 28). So an average disciplined nomad camp, with an even split between formed mounted lancers and loose mounted archers, would have a total platoon-scale BR of 84, and a max-sized disciplined nomad camp of 168, either of which is plenty to keep a borderlands count awake at night, nevermind a marquis or baron. I like that a lot - maybe Nomads are really the go-to guys for hiring in the wilderness and taking domains.