Pretty much any major at Yale will be well-funded with lots of research opportunities. The senior requirement for the Environmental Studies major is a mandatory independent research project, with a relevant topic of your choosing. Additionally, there is an optional summer environmental internship program between junior and senior year for which the department can provide some financial support. If you are interested in bio-engineering, however, wouldn't a major like biomedical, environmental, or even chemical engineering (or molecular biophysics & biochemistry) be more relevant? You generally need to gain a strong background in engineering in undergrad if you hope to become an engineer later on. The Environmental Studies major, on the other hand, would prepare you for graduate study in law, medicine, or public health, or careers in business, environmental management and conservation, teaching, and writing.
Btw, Yale has just recently announced the creation of a Biodesign Institute, which it will open in 2012. Check it out: Yale Launches New Biodesign Institute on West Campus