| My initial response is that it wouldn't be much of an issue, but it seems like you could easily prove your interesting theory by simply recording the sound of an extra (un-played) basses DI signal thats just sitting in the same room, while you play the other bass through your amp/cab. I'd think the finished recording would end up giving you a pretty good idea of the pickups bleed factor.
PS:
Set your un-played basses recording level where you normally would for DI recording, to achieve the most accurate test results.
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