fleas, Frontline and FeLV

[Lance]

One of our dogs has the tell-tale little black "nits" in the fur on  
her neck that indicate fleas are incoming. We're going to treat her  
tomorrow with Frontline. My father is convinced that none of the  
other animals should be treated if they "don't have fleas."

My Ember is FeLV+, and while she is generally isolated from the other  
animals, the one dog who has the "nits" is occasionally in the room  
adjoining ours with my mom, so that the two have space that overlaps.  
I worry about the possibility of Hemobartanella. Ember is four years  
old and currently asymptomatic. Should I treat her with Frontline,  
just in case she's had exposure?