The functionality of DLP and the Content Awareness are somewhat different.
For one thing, Content Awareness only supports a subset of the data types DLP supports.
Specifically, Content Awareness does not operate as an MTA, leverage an exchange agent, or support the advanced data types (Document fingerprint, dictionary, and templates).
DLP also has a separate policy versus Content Awareness, which can operate as part of the unified policy.
Content Awareness will inspect traffic in both directions and also work in a VSX environment, whereas DLP only does egress and won't work with VSX.