Whatever it takes to make it sound good, period.I get stuff to mix and sometimes have no choice but to blend in good samples.When I track, I usually get the results I need, but every so often in the course of overdubing/mixing..things change.sometimes a little added umph or attack or whatever is needed without using a bunch of eq,etc to get it right in the mix. ..I have a friend who produces very high profile rock records ... He prefers tracking drums at Sound City room "A"[Nirvana Nevermind ..etc,etc...], with a very nice choice of hand doctored drums,High end mics, old neve console, etc at his disposal, and he ain't no slouch at getting great drum sounds!.But sometimes he blends in samples to compete with the numerous heavy marshall, boogie, etc wall of guitars in the final mix.I learned the whole soundreplacer thing working on his stuff and believe me , when nescessary ..there ain't no shame in it, ...so long as the end results rock!
.......and yes, you Can mess with the dynamics of a sample allowing it to breath in the track ....within soundreplacer itself, automated fader rides, compression, etc..