Keith,
It has been about 35 years, but I used to work in a Seattle truck parts store where we sold Stemco products. The hubcap has three places it could leak. The red rubber fill plug in the middle, the metal screw plug for draining and the gasket. The red rubber plug can leak only if it is filled too full, the metal drain plug should only leak if it is not screwed in tight and the gasket can lean if the attachment screws are not tight. The inner seal on the back of the wheel can leak but that is entirely different.
Without looking at it, it sounds like the drain plug was not tightened when the sample was taken. Sometimes it helps if you use a flashlight, but there are fill lines on the plastic window. If the oil is up to the fill line, the bearing will not fail from lack of oil. If there is no oil, the bearing will fail quickly.
IMHO you should be able to walk around your coach and touch wheel parts, including the front hubs, and they should feel "pretty warm" and about the same. If one of the front hubs feels "an awful lot hotter" than the other, you might be heading for bearing failure. If you have been braking hard on a long downhill they will be warmer.
See you soon for the clams!