That is essentially true, but there are certains things that if implemented can make a docker more suitable for unraid, uid and gid being the main one, using the TZ variable (passed with the bind time feature from the template) in containers where timezones are important is another, although the TZ variable can be passed manually from the comnand line of course on non-unraid boxes.
If you're building a container you're on the command line anyway...