Using the Live Paint bucket is very much like clicking on a swatch in the Swatches palette. Note that even in regular objects outside of Live Paint, applying a gradient swatch to a object that was formerly not painted with a gradient applies the gradient at the default angle. (When you assign a different gradient swatch to an object that is already painted with a gradient, it keeps the existing angle, and other gradient vector attributes such as stop and start position and highlight position for radial gradients.)
To assign a gradient angle to areas in Live Paint, you select those areas with the Live Paint Select tool, then set the gradient angle while they are selected, either with the Gradient palette or the Gradient Tool. You can also apply gradient angles by selecting closed paths inside Live Paint and applying the new gradient angle, if you want to apply the same angle to all the live paint areas bounded by that path.
Just remember: select first, then set angle, not set angle then fill.