Sometimes at the end of my workout when it's been especially strenuous I notice that my fingers/hands seem tight and swollen (I don't use my hands when working out since I do primarily walking/running/hiking). Is this due to dehydration?

That tight, swollen feeling may be due to the collection of blood in your hands due to positioning during your workout. I used to engage in high-intensity walks during which I swung my arms low (as opposed to pumping them level with my chest). After 45 minutes it felt like my fingers were going to pop off! Try bending your arms at the elbow while hiking and walking so that your hands swing in an arc near the level of your heart. I'm a runner now, so this movement has become second-nature, but you'll still see walkers and runners holding their arms above their heads at the end of a workout to help alleviate discomfort. You'll get an additional benefit from bringing your hands up, too: your form will be more compact and controlled, and your arms movements will help propel you along during your walks.
Re: the possibility of dehydration -- be sure to consume some liquids (water, diluted sports drink, etc.) during your workouts, especially if you're outside in the heat.

thanks I never thought of that! When I'm jogging my hands/arms are bent and at waist level but at the end of my workout I usually walk for 10-20 minutes and I do end up swinging my hands, arms straight, at my sides, that would totally explain it!

Yep, I've heart the exact same thing...