All engineering degrees (and really all college degrees) require work and I'm not sure that chemical engineering is the hardest degree. Each degree is what you make of it and all require hard work and good time management to get it all done. Many students work their way through college and do just fine. It's all about making the best use of your time and resources. If you need to work while going to school, that just means you need to work hard on your school work when you have the time and don't procrastinate. Visit with your professors frequently and get tutoring help so that you don't get behind on your school work.
As far as grades go, you always want to get the best grades you can regardless of what major you are in. If you work hard, network, participate in student organizations or show leadership in some way, then jobs will be available. Some companies have a minimum GPA that is required so if your GPA is low, you may be a bit more limited in opportunities with those companies. BUT, again, if you network, show how hard you are working, do all you can do to get the best grades possible, then jobs will be available.