There seems to be a very strange misconception about Int'l Rumba among some American style dancers, and that is the idea that the legs are held straight or stiff with very little hip motion.
The truth is, both American and Int'l style Rumba use the same basic hip motion, achieved as a result of the alternate bending and straightening action of the knees. In both styles, you will have a moment where one leg is bent while the other is straight, and you will also have a moment when both legs are straight. The difference between the two styles is the timing of the straightening of the moving leg.
In Int'l style, the free bent leg will straighten in the instant before it takes weight. In American style, it will either straighten after taking weight, or as the weight is being transferred (depending on who you talk to).
Either way, you should have equal opportunity to exercise your hip action, as well as equal opportunity to stand tall and lifted. It's really only a difference of timing.
Sincerely,
Jonathan Atkinson