Most places, especially probation/parole departments, make it painfully clear that eating anything with poppy seeds is forbidden. So even if it was a 'false' positive it is still on you.
Dipstick tests probably can't differentiate, but more advanced testing methods may be able to; they also raised the cut-off level for opiates considerably quite a while ago (back in 1998 ). Honestly, though, that excuse is cliched. Test positive for opiates, anywhere, tell them it was because of poppy seeds and see what kind of looks you get. There are circumstances under which it might get you a pass for a re-test, but you could only ever use that excuse once before all of your credibility goes out the window (assuming it hasn't already).
Also realize that multiple tests can be performed on the same urine sample. As a matter of fact, any accredited lab is going to take your urine sample and split it into two samples before they do anything else. They could initially do a dipstick/standard test, then when you get a preliminary OPI+ result they will do a more thorough GC/MS on the remaining sample.