Yes. Have a look at the GroupWise.ItemArchive() method in the Formativ Language Guide.
You can also use the Message.Archived property to archive messages. To use the Message.Archived property, you first need to access the message object, which is available a multutude of way via the GroupWise.Account… property. See the top ‘Accessing Items in the Message Store’ in the Programmers Guide for more information on how to access existing messages.
I hope this information helps.