Absolutely not! Every account isolated using virtual containers. It is like having a dedicated server or vps without giving up your memory and cpu allocation to run services and backend. Accounts cannot affect one another in any way. If a site gets an overwhelming attack it will not affect other sites on the server. All accounts separated with dedicated cpu/ram and disk resources as well as isolated on the network level with proper protection allocation. The server cannot be overwhelmed under any circumstances! You get your protection and resource allocation no matter what.