There are no limitations, access is via admin account. However there's a code of conduct to follow:
This ACI Server resource is shared. This means that you can see other developer's resources, and they can see yours. Please, do not erase resources you have not created yourself. Do not upload very large resources or you may drain capacity from other users. Also, do not perform performance testing against this shared instance of ACI.
(source: https://devnetsandbox.cisco.com/DevNet/catalog/ACI-Simulator-Always-On)
