Yes and no. The Apple Watch works with Peloton Digital so if you're doing something away from the bike or tread it will track heart rate, speed, etc. This is especially useful for running (on a treadmill or outside), walking, etc.
Currently, it does not connect to the bike or tread as those require Ant+ format heart rate monitors and Apple Watch uses Bluetooth. My preferred HRM is a Scosche Rhythm+ arm band. If you buy one look online for a coupon as there always seems to be one available. Scosche Rhythm+™
I actually wear a scosche to get accurate heart rate to the bike as well as my Apple Watch because I like to close my rings