But they can also make it more pernicious. For example by having companies pay them so that they can train their AI on their products, with regular updates. Not technically an ad, but the AI will be more aware of their products so that they are more likely to be recommended to the user. In other words, that's paying for the right to advertise to the AI rather than to advertise to consumers directly.
Why would they ever make it obvious? It makes no sense. google just had the luck of political inaction, and eventually enshitified it further to the point where you might not know it was an ad.
To not undermine trust into their product and because ads are lower quality than organic results, and by making them indistinguishable, it will make their product worse.
The chatbot market is still competitive, and while users may tolerate ads alongside their answers, they may not tolerate lower quality answers (that is ads disguised as answers). With Google search, they can get away with it because they are still the best even with the enshitification.
There is another reason why it is in their best interest to make it really obvious there are ads. Chatbots want you to pay directly, sometimes hundreds of dollars a month, they are not getting that kind of money with ads, so obnoxious ads are also a way to say "hey look, if you pay, you won't get ads". It doesn't mean ads won't make a comeback in paid tiers later, but not initially.
So, yes, lots of "probably", but my guess would go towards the first ads being obvious and flashy rather than subtle.
it's something that continually needs to be reenforced again and again. somebody will be made example of.
E.g., around here, "happy holidays" would splash an ad for Jacobs coffee.