I started playing the marimba and although it seems a bit unusual I wish to be part of a jazz band with that instrument. Fortunately, before buying my own instrument I found out that marimbas have different pitches, some really nice ones are A=443. But I do need to get an instrument that is tuned at A=440 to fit in with a band, right?
Although lots of bands choose A=440Hz as their tuning base, it doesn't have to be.
Marimbas are not possible to tune up/down, so they are what they are. However - all other instruments (discounting pianos/organs/Fender Rhodes et al) can be adjusted. Decades ago, in bands, where there was a piano at the venue that was enough in tune to be playable, my band would tune to it - inevitably a bit low - so at least everyone was in tune. Even if there's an electronic keyboard to be part of the band, most have the facility to be fine-tuned.
So, whilst it would seem advisable to have a marimba in 'standard' tuning, if A=443Hz provides a far better instrument, I'd have thought all the other band members would be able to match that with no real problems, except perhaps for those with AP.
Not all instruments are at the same pitch. I heard a piano tuner interviewed, who tuned pianos for the big concert halls, and he said for piano concertos he tuned the piano 1.5 cents sharp. Certain instruments are tuned slightly sharp, I think the accordion is for ensembles. Also 440 is not universal, in Vienna I believe it is 442-444.
If the marimba or vibraphone is flat in relation to the the ensemble it is not a good sound. An example was on British light music radio programmes. The style many years ago was to finish a piece on a rising violin scale, followed by a vibraphone chord. Because the violins would rise in pitch throughout the performance the final vibraphone added 6th chord was often flat.
I would suggest you go on a specialist tuned percussion forum, or talk to a marimba technician. My guess is the marimba is deliberately tuned slightly sharp.