On current SPARC Systems you can choose to use LDoms and/or Zones.
Using LDoms you are able to run independent Solaris Versions on the same SPARC Server.
Dedicated Memory and CPUs makes LDom very efficient (Zero Overhead). LDoms can be live migrated to other SPARC Servers.
Solaris Zones are Application Environments running on a Solaris OS. Using Solaris Zones you run your Applications in different Versions and different configurations on the same Solaris OS.
If you are still using older SPARC Hardware, like M3/4/5000/... run your Applications always in Zones. When you upgrade to newer SPARC Systems in the future, you are able to migrate the Zones to the new Hardware in Minutes. And of course you can migrate the Zones into LDoms as well.
We have done such migration projects very successful at customer sites the last two years.
I recommend to use both technologies together to improve the flexibility in your data centre.
LDoms as your OS Platform (multiple LDoms per SPARC Server) and Zones to run the Applications.
Checkout my interview with Rick Ramsey at Oracle OpenWorld 2013