Can you confirm whether triceps exercises would engage pectoral muscles?

Both muscles are attached to the humerus, your arm bone. Triceps do not directly have anything to do with the breasts. Of course moving your arm with the triceps will also move the pectoral muscle. 

Triceps Kickback excercises do not technically 'workout' your pect muscles but you are using yoiur pect muscles in a supportive way.  If you are eager to workout your triceps and completely isolate your pect muscles the best way is to use a bar/cable system for triceps 'pulldowns'.  As long as your elbows are locked against your sides then your triceps are isolated.  That said, why push it?  Unless you're working with someone who hands you the bar then you're bound to use your chest when setting up for the exercise.  I promise that, whatever your situation, taking off a few weeks from strenuous upper body exercise will benefit a result that will hopefully last you many happy years.  In the scheme of things the advantages of waiting a few weeks will far outweigh any short delay in gym time.

First of all, at one month out it might be a little early to start vigorous upper body exercise.  Check with your surgeon.  As for triceps kick backs, when done properly and with light weights that exercise does not "engage" the pectoralis.  The problem is that the arm movement will stretch (not contract) the muscle and at one month out may be uncomfortable or even painful.  The second problem is on the return--i.e when the arm returns from the extended position.  When done incorrectly and with a weight that is too heavy, then the pectoralis contracts involuntarily to keep the arm from simply flailing back to the starting position.So, bottom line;  check with your surgeon, and if you do that exercise do it properly and with light weight.