2001 Toyota Sequoia Shimmy

Wheel bearing usually don't cause a shimmy. I have seen some that are very loose and did not make any noises when driving.
You want to make sure your steering and suspension is tight, no play in bearings or joints.
Do you have aftermarket rims on this vehicle? About what speed are you traveling when the shimmy occurs?
Does the shimmy have all the time or only when braking?
There are several components that can cause a vehicle to shimmy. If you have any loose steering components including the steering gear, tire tread the is abnormally worn or deformed, out of alignment (specifically with the caster angle measurement), tires out of balance, rims that are not centered on the hubs. You could try rotating the tires the front tires to the back and rear tires to the front to see if that changes anything?

Since you had the alignment done and the tires balanced I'm suspecting what is called tire "sidewall stiffness variation"
Most tires have a variation in stiffness or springiness to each tire. Manufactures attempt to reduce this variations in tire construction. Because of this variation (typically in the sidewall) the tire has a stiff spot which will cause a steering wheel shimmy at high rates of speed. In these cases it is best to have the tires balanced on a high end tire balancer. Hunter makes one of the best tire balancer machines on the market, its call a "road force". This tire balancer will load the tire as it is spinning and detects any tire stiffness variation and can calculate where to add weight to counter balance these differences in the tire. Other tire balancers just spin the wheel/tire and calculates out of balances only. So even though your tires maybe balanced the variation is still there and has not been counter balanced.
Answer my questions and I hope I answered you question

Since we know the rims are centered good because they're stock and none of the rims are bent. All signs point to tires causing the vibration at highway speeds. If you have cupping on the tires or an aggressive tread pattern this too will cause a vibration.

The only way to really know if it's your tires is with the "road force" tire balancer. Having the tires balanced with this machine should take away any variation in the tires to stop the shimmy.

If I remember right the brake system that is on the front of these vehicle is what is called a "fixed caliper" which means you're going to feel any warpage in the front rotors that much more than the "floating caliper" design (this brake caliper floats and absorbs some rotor warpage.
So, yes a warped rotor will cause the steering wheel to shimmy but only when applying the brake pedal, not all the time (higher speed like 65-70 will exaggerate the shimmy).

You'll have to call around to find out who has the road force tire balancer. Some tire shops have them but I would guess more do not (cost is around 13,000 -20,000).
To positively identify a warped rotor we use was is called a dial indicator. This tool will reads movement from 0.001 or 0.0001 of an inch on the friction surface of the rotor to determine if rotor(s) are warped.
I hope I answered you question let me know what you find.