Facebook announced today that it has acquired Seattle-based stealth hyper-local mobile advertising startup Rel8tion. The team and technology could help Facebook start to shows ads to its 200 million mobile users.

So far, Facebook has only monetized mobile users through its location-based promotions system Facebook Deals, which shows users and their friends discounts at local businesses when they check-in through Places. With advertising on the web interface generating the bulk of Facebook’s revenues, it is reasonable to believe mobile advertising could become a similarly important stream.

Facebook has been pushing users to list their current city as well as their work place and other personal info lately. This info could be used to power location-based advertising.

Rel8tion’s engineering team will join Facebook’s Seattle office, and one of its founders, Peter Wilson, will become an engineering director. Wilson was formerly formerly a Google engineering director and a long-time Microsoft employee.

Other Rel8tion team members include founder Scott Hannan, previously the VP of Business Development at Pelago — makers of location-based social network Whrrl, and CTO Nat Brown, formerly the CTO of iLike.com and VP of Technology at MySpace’s Seattle office.

One obstacle to monetization of Facebook’s mobile users is that they access the site through a wide variety of interfaces, apps, and devices. Without a consistent space other than the news feed in which to serve ads, Facebook will have to come up with an innovative way to put Rel8tion to work.