It's probably not great for this. Resting heart rate is correlated with fitness, but candidates can be nervous during interviews which can drastically change their heart rate. You'd probably be able to make better guesses about their health through looking at them (do they look sickly or overweight?) and interviewing them.

It's also not a specific enough signal for the types of health conditions that require taking time off work. Assuming they could get an accurate resting heart rate, most of the time it'll just indicate whether the candidate does a lot of exercise.