What is the business model of product placement startups like Roamlike?

Maybe? How about asking the brands you're seeing be advertised in this way. They should be very willing to talk to you if you ask them something like, "Hey, we're considering using ___ service. I see you have been doing so. What has your experience been like?" No better information than first-hand information. Why ask us when you can ask those real customers what it's like?

You can interpret those customer responses as an indication of whether the model is likely to be viable. As for the other questions, make money is the goal. Sounds awfully sketchy to me, otherwise hoteliers would have been doing this for decades.