Yes but not exactly cheap to do. Roland make the GK3B pickup for bass ( see http://rolandus.com/products/productdetails.aspx?ObjectId=563&ParentId=53
) but you also need the GI-20 GK -> MIDI interface ( http://rolandus.com/products/productdetails.aspx?ObjectId=563&ParentId=53
) that converts the signal from the GK pickup to MIDI that can then be sent to a module or keyboard. The advantage of the GK pickups is that lag is not a problem.
As for pitch -> MIDI devices they are limited ( like the previous message said ) to a single note which is probably not so bad for bass, but they do suffer badly from lag that makes them hard to use with normal playing.
The GK pickup is really the only practical option but does come at a high price. That is what pro players use to trigger MIDI devices from guitars.
[This message has been edited by Nigel (edited 04-12-2008).]