I have not, but I have worked with the LiveLink APIs quite a bit (up until December 2005).

Back in 2005 (LiveLink version v7.x?), OpenText's LiveLink objects (web-based workflow, document management, records management, UI, and related meta data features) all were database driven (SQL, Oracle, etc.) and could be extended using their 'oScript' language and Livelink APIs (aka 'LAPI'). 

Given this design/flexibility, I don't forsee any issues integrating K2 functionality with LiveLink.

Do you have a specific LiveLink functionality you are looking to integrate K2 with?

I suspect it wouldn't be too simple...is is more of a cost/benefit evaluation (volume of LL processes to be converted to blackpearl, complexity, etc. versus the time it would take to custom code the LL->BP conversions). 

It's beyond my expertise, but 'hypothetically', Id'd think that given that K2 blackpearl is based on WWF xml/xoml structures, you may be able to poke inside the LiveLink workflows using the LAPI API calls or via direct from the LL databases (likely not supported by OpenText , and convert the data into valid XOML structures, then consume them in K2 to convert/merge them to valid K2 processes.

Just a thought. I don't recall this being attempted yet...care to be the first? ;-)