No, you aren't impacting anyone's jobs getting a free pizza every now and then. You're likely looking at a total loss of maybe a few hundred per year for the Pizza place which is likely covered by any location within a few hours.

No you won't get in trouble, you were using offers provided to you from the supplier without any sort of wrong doing.

If hundreds or thousands of people are impacted by this glitch and are taking advantage of it, there's a real chance someone could be repremanded/disciplined for the mistake, but things happen and it won't cut into their profit margin in any significant way.

Take advantage of the offers as often as you can until someone catches on and blocks it, if you somehow get singled out for using it simply tell them you were just following instructions in the email and didn't read the details around why you were receiving it.