You can totally use emojis as passwords. You can probably even make this a policy at your company.
Edit: I thought this was an obvious enough joke, but just to clear things up: Only do this if you hate your company and everyone working there.
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The times I calculated were indeed going over every possible combination, it would take half as long to crack a password on average. Considering reducing the time to 1/1000000 still leaves you with an incomprehensibly large estimated timespan, dividing that by 2 doesn't do that much for making it brute-forceable.
I did note it was specifically for 8 emojis, not 8 characters or bytes.
And yes, it's very impractical and likely to break things. It's better and much easier to add extra letters, numbers, and symbols to your password rather than using emojis. Using a password manager is even better.
As you stated, a single unicode character would mean your password wouldn't be included with the potential options in almost all brute forcing tools. Whether you use 8 emojis or 1, your password likely won't get brute forced.
All of my "emoji password" numbers are if the attacker knows it's a password containing exactly 8 emojis, and nothing more. Adding a regular symbols+upper+lower+numbers 16 character password would make it even more impossible to brute force.