I work for a natural gas utility that also supplies propane, although I'm primarily in the natural gas end of our company here's my view, first off for a 100 pounder it took a good hit to take a dent, second, to get a brand new tank filled the first time it needs to be purged...at an extra expense above having it filled which means it is now YOURS with no option to return it.
now here lies the problem...each individual that fills that can make the decision to not fill it because of the dent.
if a guy tells you, yea just always bring it to us....we'll fill it, that's great, unless they close or change management. then who knows, you may not find anyone to fill it. personally if it was me I wouldn't risk the cost in a #100 tank that arrived with a dent on not having someone fill it with no questions asked where ever you take it.
that being said, I don't know how big the dent is or the location of it on the tank. if it's small and on the side not near a weld you should be ok. but like I said, there not cheap...and it shouldn't have a dent.