OLEDB Wait Type and Functions
OLEDB waits cover a variety of states, including (but not limited too) client-side profiler traces, some DBCC commands, materialisation of DMVs, possibly some full-text functions in 2005 (IIRC, most have been split out to FT specific waits in 2008) and also linked server queries as you mentioned.

I'm not aware of UDF functions inherently resulting in OLEDB waits, unless they are performing one of the actions I mentioned above.

Rather than looking at the raw percentage wait time attributed to OLEDB, have you checked the average wait time per wait? It may prove to be so low as to be insignificant.