With all the mutations going on, no one can say with 100 percent certainty what is safe. Your statement is true for the known strains, except maybe the Reston strain, which hasn’t caused symptoms/death in humans so far as I know.
The recent Science publication found fewer than 400 mutations, and more than half of them were conservative, meaning that they changed the genetic sequence without changing the protein sequence. This is out of a genome that is around 19,000 bases. So it really has not changed very much at all.
The Reston strain has been documented to cause asymptomatic disease in humans--15 people were demonstrated to have seropositivity, evidence of past infection. It is still treated as a BSL-4 agent, since there is still the possibility that it causes disease in humans as severe as other strains of Ebola do.