I'm guessing it's just how CB Juice is importing them then since normal CB registration and user creation is working fine. We'll eventually have import/export tools built in, but that won't be until a much later release. Below is the updated API usage for registering a user, but I'm unsure if CB Juice is using it or older usage.
www.joomlapolis.com/forum/153-professional-member-support/228495-solved-cb-version-api-cb-version-205#258806
Specifically activateUser function is what sends the pending/welcome emails.
To force User Management to regenerate the password and send the email you need to have "Generate Registration Password" set to "Yes" within CB > Configuration > Registration. Next the user must be Approved or it will not send. Now approve them and it should generate a new password then send the Welcome email.