I'm not sure that this makes sense. What is this "open tagging solution?"
Yojimbo is a database. You put documents in the Yojimbo database, and then you can tag and sort them within Yojimbo. Yojimbo contains and manages these documents. Note that Yojimbo _does_ also make its internal data available to Spotlight, so if you do searches within OS X, you will see the results in its searches.
However, at this time, there are a few (major, IMO) downsides to Yojimbo's Spotlight integration:
1) Tags aren't used. It's just contained text. So if I have a few tags on a Yojimbo item, and search Spotlight for those tags, they will not appear (GRRR)
2) Yojimbo doesn't support Quicklook yet, now a year after Lion shipped. So if I get a Yojimbo result in Spotlight, I get an icon and a big blob of the form GUID.yojimboitem. I cannot see what the item is without opening Yojimbo.
But do note that a "standard tagging solution" really doesn't mean anything. There is not any agreed upon standard: OpenMeta may be "open" but it is not native functionality in OS X, and I don't know how it would really make sense in a database application such as Yojimbo anyway.