In an intrinsic semiconductor, are there the same number of carrier electrons and holes? Or this is just exclusive for silicon?
In an intrinsic semiconductor the electron and hole concentration are equal. But you almost certainly don't have an intrinsic semiconductor.
Semiconductors are sensitive to impurity concentrations on the order of parts per billion or parts per trillion. It is very difficult, and therefore very expensive, to approach a true intrinsic semiconductor. Polymers that behave like semiconductors sound to me like they are likely going to have unavoidable impurities or dangling bonds that change the carrier concentrations.

then for Jp should I divide the total J by 2 or does this only apply to inorganic semiconductors?

This doesn't apply for any semiconductor. The mobility of the electrons and holes will be different, which you can't figure out as easily as you propose. I believe Hall measurements are a common method for measuring mobility.