You can check this article by Mick2009:
https://www-secure.symantec.com/connect/articles/sav-linux-somewhat-illustrated-guide-part-3
It states:
"As long as the SAVFL client is updating every day, the files downloaded will be of manageable size.
If the SAVFL client goes out-of-date by weeks, then a full set of definitions will need to be downloaded. That can be a couple hundred MB."
So yes, this means it should use deltas unless it gets weeks out of date in which case it will than download the full set.