Would rim brakes help a slightly bent rim? After recently falling and bending the rim a bit I was wondering if forcefully applying the brakes while in motion help it straighten a bit? 

Might be my imagination but it seems much truer than right after the fall after constantly applying the brake.
The short answer to the question is, no. 

Consider and compare the braking force to the other acting forces, and which would overcome the other; drive side and non-drive side spokes pulling radially and laterally on the wheel (this can be quite a high amount of force when adding all of the spokes together. It takes all of your weight, as well as any impacts you sustain while riding.) Rotational force and momentum is another major factor, and it is often at or well above your weight. The amount of force that a road caliper can apppy (or any caliper) is well below any of these other forces. A disc brake may be an exception, since I've heard of extreme circumstances in which a disc brake could actually rip a hub from a rim, but that has little to do with the lateral true of a rim.

Another component, directly related to you question of being "in motion", is that the braking power of most calipers is not perfectly symmetrical, because of caliper design or because of imperfect setup. With these asymmetrical and off-center forces, the rim is often pushed to one side creating a high/low tension in the spokes between either side. The asymmetrical and off-center force also create a certain amount of twisting in the wheel that has a similar rotation as that of the nipples threading onto the spokes. 

In essence, braking always has a deteriorative effect on trueness.