They do seem to be interchangeable and are used as such in a lot of cases. Though there are some cases where it seems they are not. To-wit:"Ineluctable" seems to be almost synonymous with "inevitable", but I feel there is a subtle difference, which I find hard to express. Can anyone clarify?
:like:So I'd see inevitable being about something in the future, whereas ineluctable is to do with a current or past position.