Here's a little experiment: Rock on up to a personal trainer and tell them that your hamstrings are really tight and seek some advice about how to fix the issue. What do you think most would say? On doing this little experiment I had 100% success rate with this one - said PTs would show you "some stretches" so you can "release" the hamstring muscles. In some cases, this would be an appropriate solution but sometimes tightness relates to a bigger fish in the ocean.
One thing I do as an exercise physiologist is a fair amount of postural analysis. The best way to do this is to observe someone in their natural state, standing, walking around, running if you can. Soon you can begin to get a good picture of the 'state of the nation' before you even do any formal exercise assessment. The joints that are the most telling are the hips, shoulders and ankles - ie joints that have multidirectional movements. Knees and elbows tell relatively simple stories in comparison.
Most people, due to genetics and to lifestyle factors (such as sitting a lot - shortens the hip flexors) are in some form of pelvic anterior tilt. This is where the top of the pelvis (anterior iliac spine) tips forward relative to the spine. This causes excessive curvature of the lumbar spine, shortened tight hip flexors, quads and adductors. Many of the activities we do in the gym are hip flexor dominant - think step and cycling for a start, the way most people squat doesn't help. So think for a minute, if my hips are shortened excessively as my pelvis is being pulled forward (think of the posture of a normal weight person who has a distinct lower belly pooch), what is happening to the hamstrings? They're likely to be in full stretch trying to keep the hips from shortening even further. The worst part - glutes and hamstrings are switched "off" because they're at their full stretch and at their weakest. Ever done a bicep curl from a straight armed position and been able to lift way more when you start with a slightly flexed arm? Try it and see for yourself!
So the answer to the hamstring tightness question may be more complex - you may need to do more hip flexor work combined with glute strengthening and activation work to take the tone off the hamstring. Completely the opposite to what you thought!
To cut a long story short, if you have a dinky pelvis as well as tight hamstrings, you pronate and your knees are internally rotated when standing naturally, I can pretty much guarantee your issue will be anterior pelvic tilt. For the figure athlete, too much anterior tilt gives the impression of the dreaded "pancake" butt.
Often traditional bodybuilding routines, whilst delivering size to muscles, lead to injury and horrible imbalances later on down the track. If you want to increase muscle mass and you want to do it for the long term, seek out an exercise physiologist (like me) or a good physio who does pilates and treats pelvic problems to do a thorough assessment before starting. It just may be the best money you spend for long term gain.
Here's a link to an article by Mike Robertson (a biomechanist who I have buckets of time for) about Hip Function (just skim over the sexist porno like pics) that will show you some illustrations of APT and exercises to help address the problem. It also deals with posterior pelvic tilt which is seen, but not as often.