Well first things first - re-awakening a year old zombie thread is not the smartest thing to do. Sometimes they get all feisty and try to chew your face off.
Depending on exactly what you are trying to do you have several options.
If you are running Scratch2 - the Flash based abomination in the eyes of Nuggan accessible on your Pi main menu as 'Scratch2' - then you will have to read up on using the external interface. I dare say GHP can help here.
If you are running the older but faster NuScratch (accessible from the same menu as 'Scratch') then you may have more options. I didn't include sensors like the DHT series in the built-in gpio server because nobody seemed to want it at that time. GHP almost certanly has it in his system that works with NuScratch and quite possibly SimpleSi's ScratchGPIO system will handle it.
If you're really serious about using it an other sensors and want support adding to NuScratch, feel free to offer some financial support for the work and it shall be done.