Viktor's ultimate is reliant on him having direct vision of you so moving out of sight behind a corner or using opaque deployables(such as Inara's wall) will prevent him from selecting your location.
If you go mid-range or short range, Vivian will shoot you down. You're better off keeping your distance. An advantage you have over Vivian is that your heavy blade goes through shields.
Makoa's shots will halven in damage before beginning to fall off at 65 units. Memorize this distance and stay out of it to render him ineffective at damaging.