Physics claims that if the pipes are the same size and there are no leaks in the inlet system they should be darn close (ignoring turbulence, etc.. which would probably have marginal impact, although fluid dynamics is complicated so I reserve the right to be wrong). Practically speaking the two caveats I added could affect the real world results, as could the other factors that I'm thinking probably don't matter (but could).
If your outlet is a reasonable length of pipe (say 2'+ or so) it removes ~most of the chances of getting false readings due to turbulence or dead spots from weird exit airflow patterns (or simply move your measurement device around the opening and if it reads the same at multiple spots its probably ok
)