Almost all new positions are for engineers, and it is noteworthy that some of these bodies are designed to address Siri's relative weakness in general issues. So there are entries for Siri software developers who, for example, deal with "general knowledge" and the "knowledge graph". Other notable recruiting efforts include a machine learning scientist and several engineers to address areas such as Proactive Intelligence (Siri's ability to anticipate information you might need), the SiriKit developer framework, and voice generation.
There is only so much that you can deduce from Apple's hiring campaign, and it will likely take a while for you to see the results. Even if Apple immediately filled every opening, it could take months or years for its influence to appear in Apple's software. However, the existence of this recruiting anger says a lot. Apple knows that Siri needs work and is ready to invest in the brain power needed to improve his AI helper.