I can't talk for other users, of course, but I'll try to give you some kind of "official" point of view :-)
Our samples are delivered as pure as possible. This means: The only filtering and EQ-ing we apply is to get rid of obvious interferences (like low-frequency rumbling or other noises) or stuff like resonances that stand out from other notes. In some cases, a sample stays almost untouched; others undergo a meticulous and time-consuming mastering process.
For our users, this has two consequences: On the one hand, all options are still intact to sculpt the sound to one's needs (... some pieces will ask for a direct, maybe more "raw" sound of a solo instrument, while another, huge arrangement, needs a broad, fat and breathy sound). The second example, on the other hand, could need some serious housecleaning to save the mix from being overcrowded, frequency-wise. Here you will grab a good EQ and maybe even some dynamics processor to bring the piece you're working on into shape.
In short - if you feel the the piece you're working on could be easier in the low-end, don't hesitate to clean it up a bit. The worst consequence could be that you decide to switch the EQ off again at a later stage. :-)
All the best,
/Dietz - Vienna Symphonic Library