A plea in abeyance is not a conviction, therefore it does not have to be disclosed on an application which asks about prior convictions.
The whole purpose of a PIA is to avoid conviction. If an employment application is more detailed beyond asking about "convictions" it may need to be disclosed. It really depends on the employer.
As the other attorney mentioned, a PIA is not a "conviction" if it's completed successfully. Before the case is dismissed, I think it would be considered "pending" however. I believe, technically, the PIA period is not considered "probation" but it is very similar, so I wouldn't be surprised if some people even in the court use that term. The best thing to do will be to get your record expunged. You'll be eligible 30 days after it's dismissed. That way you don't have to mention it at all.