Not necessarily. If any unsafe constructs are locally visible during code review, and the language is such that unsafe constructs are rarely required, then it's much easier to give unsafe constructs a higher level of scrutiny that you can't afford to do in a language like C where unsafe things are pervasive and the same line can easily be safe in one context and unsafe in another.
I don't know about SystemD's code policies. But certainly serious vulnerabilities have been found even in C code where changes went through code review (the famous Chrome sandbox escape due to an undefined bitshift was noted to have been reviewed and explicitly "LGTMed" by two people).
And the decision about whether to code review is not necessarily static. A language that reduces the cost and/or increases the benefits of code reviews changes the decision space. And a more expressive language can free up developer time to spend on things like code review.
