Yes, you can use MJ on dev/test domains, there are two side effects only:
1) Remote device detection doesn't work, but in this case MJ uses a fallback to local device database (AMDD), so most of mobile devices will be detected correctly (unfortunately, Mobile-AMDD plugin doesn't support tablets),
2) A support ads may be displayed on Mobile_Basic template.
To avoid above side effects, you can contact us by email and ask to whitelist those subdomains (don't forget to mention your main domain and subscription's id).