If you want to get technical then weights are incredibly relevant to hiking fitness.
As well as being the very best thing you can do for injury prevention and joint stability (as you rightly said!) weights can lead to two extra great benefits - increased movement economy (i.e. every step takes less energy) and improved strength (making stairs and uphills significantly easier).
Beyond that (particularly if you have a dodgy knee) any type of lower impact, long duration exercise (things like swimming or cycling) can have a good cross over into hiking fitness as well.
And then of course there are always things like loaded hill intervals when you want to get really serious
