This chapter from Remarkable Conversations called "Deafblindness" will clarify you why a person who is deaf and who is blind is deaf-blind or deafblind. This is the link to the chapter:
In regards to your second question: yes, a person who is deaf-blind also qualifies for low-incidence funding.
Topic: The importance of having the disability of deaf-blindness “checked” in the IEP
By Gloria Rodriguez-Gil
Subject Re: RE checking deafblind on the IEP