Again, thanks to everyone for posting their opinions.
The FHA guide is pretty clear that if there is a lease in place, then the property rights have to be addressed as leased fee. Check Appendix D of the FHA guide. If the property owner is receiving income from the property, then it is leased fee. They use an example of a 2-4 unit property that includes both owner-occupation and tenancy; they state the property rights are leased fee.
In my experience, if the property is vacant, this represents a fee simple estate, even if the anticipation of the most likely buyer were for renting the property to tenants. When determining property rights, the theory of anticipation is abandoned. Personally, I disagree with this momentary lapse of consistency, but you can only run head-first into a wall so many times.
As far as a leased fee analysis goes, if the appraiser determines through research that the difference between in-place and market rent is so negligible that a purchaser would not make a distinction between leased fee and fee simple, so be it. Just say that in the appraisal.
With regard to the approaches, the appraiser should follow the market. If a typical buyer would not research comparable rents in the market, then disclose that within the report to explain why the Income approach was not used. That being said, an appraiser should not use that as an excuse not to do the work. I found that Craigslist has been a pretty handy tool for finding asking rents in a market; however, those in rural areas might have a more difficult time.