A company that wants to monetise fedi will likely not get very far with plain ad accounts. They will just be blocked en masse.
Likewise for "influencers": they will be treated with suspicion.

So companies will likely resort to covert marketing strategies: someone will ask for recommendations on a product, and others will subtly drop names in the thread.
This already happens without ulterior motives, so it will be hard to distinguish the two. A whole operation can be carefully orchestrated.

There might be equally subtle product placement in images and links posted.

I have no doubt this already happens on other platforms as well, but because on there ads an influencers are effective, it is likely a low-key activity.
I think soon, people will start to make a living from this kind of activity on fedi. Commercialisation of fedi will be insidious.