I have several pictures stored on iPad when I update to 4.1 will the update erase all pics even if they are in iPad app Stash Pro?

I think its always a recommendation to backup first before doing anything which will call for any internal or external change to a device. If your Stash pro supports(it should) itunes usb file transfer,then you should immediately copy down all the pictures and data to your PC/Mac and then do anything you want with iPad. Same applies for all the apps that hold or contain any important data or information that you don't want to lose. Update often just erase the firmware and replaces it with new version,nothing done to anything else,but it is very frequent that after updates many apps seem to crash and doesn't work as expected so you are supposed to delete and reinstall them in which process the data stored in them get lost. So please backup first then update.