I personally dont have my walkins temperature monitored yet, although it is a feature i am planning to do. I do have the doors themselves monitored so that i know if they were opened if the alarm goes off.
I think it would be a good idea, although i’m not too sure how much they would cost you to set up. the last i checked the temp sensors ran about $200 each for me to purchase.
One thing you might also consider is having your alarm company contact you if the panel ever loses power. Its not as good as having temp sensors in the coolers, but it might be a cheaper alternative. On mine, If the building loses power for more than say 20 or 30 minutes, it calls in to the monitoring company and lets them know, and they then call me to let me know so that I can come down and ice everything down if need be.