I mean.. you could, but I advise against it. Standard TTS (like that in windows) has a very robotic quality about it. It's very easy to tell that it isn't natural speech due to the lack of intonation and contextual cadence. In other words.. it lacks all the magic of tailored voice acting, which is the primary point of VA in games.
I could be wrong, but I expect most people would prefer to have no VA, compared to TTS audio. Personally, if the VA was TTS, that would completely shatter any chance of immersion and would just end up being distracting. So I'd just mute it anyway.
Having said that.. there are more advanced options for TTS that could possibly, maybe, potentially be acceptable and even "pass as real" in some contexts. They are mostly paid, however, and not free. And the quality varies wildly. The only one I am familiar with is a service called CyberVoice (It was used last year to create synthetic voice lines in Geralt's voice for a mod quest, and it was impressive).
