keybase pgp verify -m "message"
You may import from Keybase to GPG easily and then perform whatever cryptographic actions you want.
# using curl
curl https://keybase.io/[them]/key.asc | gpg --import
# using `keybase pgp pull` which
# imports to GPG key chain for you
keybase follow [them]
keybase pgp pull [them]