Truth is, no matter how noble your intention is, you must first discuss that means of payment to the employees. Otherwise, they're likely going to kick against it and see it as dictatorial on your part. And they will be absolutely right to have that conception of you in that regard if it happens so. By letting them know ahead, you would've sounded the caveat to them on the downside of Bitcoin too. So they know whatever comes out of it in dip immediately payment is made won't be your fault.
Well, I'm not sure I understood well, whether the owner wants to pay salaries in BTC or wants to gift BTC to his workers as some bonus!? I guess if it's the first one then he should listen to his employees and what they have to say about that, if it's a gift then workers should accept it and be grateful for such a good boss! As you say no matter how noble intentions are some people depend on their salaries and they don't wish to invest further, they need cash to survive through the month!
I think that giving bitcoin to your employees as a bonus or incentive is much better idea, like what @GreatArkansas have mentioned above. It would be more effective as well in accordance to your intention of helping them save for the future. Moreover, this could encourage them to seek on how does it work in order to reap the benefits of what you have given them.
If the owner can allow himself a bit more expenses for the happiness of his workers then this would be the best choice!