Grapevine is still very new to the scene. There are apps like Blind which have been active for 5+ years a have started monetizing recently.
They are still in the 0-1 phase where bringing traffic to the app is topmost priority.
For monetization, apart from ads, they might start a job portal section (taking cut from companies) since they have a good pool of working folks who can apply to these jobs.
Also, they can add a section for adding salaries, something like levels.fyi and provide folks with salary negotiation help (take a cut if it's successful). Providing data to third parties can be another stream of revenue.
I guess I know some of the grapevine co-founders (but they don't know me :P).
Pretty sure they are gonna make something epic !