I'm having trouble seeing valid grievance that will produce anything. Perhaps there's something in your local, but I am having trouble seeing any tangible result from a grievance at this stage.
The timeline is a little muddy for me without all the dates, but my understanding is you were on "vacation" the week ending 3/16/13. There should have been a check reflecting that no later than 3/7/13(as you state you get paid on Thursdays). There wasn't so company fault there.
Article 17 3rd para 1st sentence
Wages for properly selected vacations, in all instances, will be paid to the employees no later than the workday prior to their vacation.
If you had let the company know immediately, or at least right after coming back from the vacation, instead of 2 weeks later 3/21/13 the company might have acted differently instead of just putting it in with the current weeks payroll to be sent out on 3/28/13.
Article 17 3rd para 2nd sentence
If the employee does not receive his/her vacation check, the Employer will make all reasonable efforts to provide the check the following day including delivery by Saturday or Next Day Air.
Reasonable is the key word. By waiting 2 weeks to let management know you basically said to them, "Hey, I wasn't paid but no rush getting it to me." Management acted in accord to the sense of urgency you gave them so they just added it to the very next paycheck you'll get.
I don't know why they didn't cut it as a separate check, but they technically did not short you any pay. Taxes are a bitch, but the company still paid the full amount before taxes were deducted so what exactly are you trying to get from this grievance?
Really, I'm with you if the company had shorted you time or pushed off paying you for weeks after being notified, but I'm just not seeing what a grievance will accomplish. I can really see management at the hearing for the grievance being "We paid you after you waited weeks to let us know you weren't paid right and now you're going to complain the government taxed you?"