IMO, if the keyboard player fulfills a bassist role, then it is a good idea to use a bass amp! This way, at least on smaller stages you're sure that the bass will be properly present everywhere on stage. With wedge monitors alone, you rely on the mixer to properly distribute to everybody individually. That's not really a standard scenario; you may well end up with either a tinny, unsatisfying in-the-face sound, or just undefined bleed from the PA.
Another advantage of a bass amp is that it will already be connected with a DI, have a channel that's set up for bass, and so on.
If available, using a low impedance input can make sense. High-impedance inputs are a special configuration that only really makes sense for passive instrument pickups, like those on most bass guitars (even more for piëzo double bass pickups).
All active sources like audiointerfaces have low impedance, which basically means they don't care what impedance the input has, so often it just won't matter at all. However, a low impedance input may reject some noise problems.
An audio interface will offer rather more level than a passive bass, but not necessarily more than an active one. If you don't overdo it with the gain, you should be fine, but just try it: a decent bass amp should sound quite nice gritty if you overdrive the preamp a bit.
At any rate, make sure to test it with another bass amp (or at least guitar amp), beforehand! There may very well noise problems, especially if the laptop is fed by a not so good power supply. If you hear an annoying static sound (often, this comes out a bit like weird rattling / drum roll), then a DI is probably the way to go. (Note that you can also go from a DI – with isolated phone output – into a bass amp instead of straight to the PA.)
Software side, I would recommend to make sure you don't have any amp simulation already in the computer. The bass signal should be bright and clear at this point, perhaps even a bit acoustic-guitar like if you listen to it with headphones. You can always reduce treble at the bass amp if necessary, but if the signal is too muffled to begin with then you may get the problem of indistinct rumble with no proper tone definition, when it gets loud on stage.