It probably isn't that big of a concern for the band, but it might be wise to ask them. Like so many styles, modern polka music has evolved. I play six or seven polka gigs each year with a traditional polka band, and I play upright bass on those gigs per the leader's request.
We've played some big Oktoberfest gigs that had many legit polka bands on the roster, so I've seen quite a few top quality international polka bands and the bass players were playing a wide variety of basses. Only one band still used a tuba player, and he doubled on electric bass. I remember seeing exotic six string basses, Warwicks, Fenders (mostly Fenders) and a few other brands. Nobody seemed to be trying to cop a tuba sound. The backline on most of those gigs is usually an SVT, probably because that's what the sound company provides for all of the events they are hired for.
Some of the bands I've seen are really top quality with killer singers and versatile players. One guy even doubled on alphorn. It's more about the playing than the bass.
I'm not saying you shouldn't try to cop a traditional tone if you think it will be beneficial, I'm just saying it's probably not as important as it might seem.
