Can someone with a pacemaker wear an I watch?
Sure, it won't hurt you or the watch but the watch may not work as advertised. AF detection probably won't work as designed and it may not give accurate heart rates. The i-Watch has some inherent problems that make it less useful for its designed purpose (detection of AF), too. IMO, a Kardia Mobile is a better/cheaper solution but it's not as handy.
OTOH, some have good luck with them and you can learn to read simple EKGs yourself, even if the "automatic" functions don't work very well for you.
My Apple Watch is my best friend when it comes to knowing what is going on. I also have a St Jude PM. The heart rate tracking is very accurate and logs details during (and slightly after) workouts. If something feels funny the EKG is an amazing tool to see what is really going on -- and create a PDF for the doc. It also has alerts for too low or too high rates. 99% of the time I don't need to know, but when I want to know the watch gives me what I need.
You know you're wired when...
Bad hair days can be blamed on your device shorting out.
I have an ICD which is both a pacer/defib. I have no problems with mine and it has saved my life.