If it's 30 minutes walk from DLP, it must be Val D'Europe?
I agree with Cwis, I am not sure how wel lit these areas are at night, but I wouldn't feel comfortable. I'm sure it's safe, taking normal precautions in mind, but I wouldn't do it. To walk from a station to your hotel is fine in the surrounding areas.
Disneyland Paris is actually not "close" to Paris indeed. It is 32 kms (ca. 20 miles east of Paris).
It can take between 30 and 45 minutes by car or train according to the type of transport you use and the trafic.
30 minutes from the park might be Val d'Europe or where contracted and associated Disney hotels are.
In any case, the area is rather safe the only thing is that except a huge shopping center opened untill 8pm, local train stations and fields there is nothing much to do in the evenings except anything related to Disney -like Disney Village-.
Alternatively, you can go to Paris but will need to consider the journey time (especially if you use train. The service stops around 12 am to go back to Disney area).
There area around Disneyland sure is safe but it's not made in a way that makes walking anywhere from DLP a good idea. You would wanna use the train/bus to the next city unless you wanna walk along a barley lit street with nothing but grass around it.