Must I credit others' published research when using it in a proprietary product, if doing so would be bad for business? If a company was building a product that uses methods designed and outlined in a published research paper, should credit be given? If crediting them would be a bad business decision, is it OK not to?

I am building a product that builds on research published by a university research group. The research outlines a quicker, cheaper and more efficient method of doing something that usually can cost much more. So it is basically just a small part of my overall project, although it allows me to cut costs drastically. The method is not patented, and the group most likely does not plan on getting a patent as they make it clear that their research is in no way related to any company or products. 

I do believe in giving credit where due, but publicly disclosing the research method that is allowing me to cut costs and release an existing product a lot cheaper than competitors would be shooting myself in the foot. 

My original idea was to make the hardware opensource, and then just sell prebuilt versions for a good price, although after seeing what is going on in the 3D printing industry - like MakerBot filing patents on their 3D printer and scanning - I am not sure if it is a good idea. 

So without opensourcing the hardware, it puts me in a difficult situation. I would like to credit the researchers, but doing so would be a bad business decision. Would it be considered acceptable practice to use their method without crediting them?
Since business is on your mind, before ethics, you should first check whether there are any legal restrictions on the use of the published research, or obligations arising from such use, issues that may depend on the applicable laws of some specific country. For example, it may be the case that you may not need consent to use the research results, since they have been openly published, but you may have some financial obligations if you are to use it for profit (and not necessarily towards only the research team), patent or no patent. So make certain where you stand.

As for ethics: it is rare for businesses to credit researchers. Instead they usually contract them either for royalties or to secure further development, if there is such potential, and not leave it to fall into the hands of competitors. "Credit due" may be one of the currencies in academia, but "money" is the currency that businesses understand. 

By contacting and maybe contracting the research team (after doing your legal due diligence first), you may even be able to secure such exclusive use of their results, or some even more efficient version of them. Again, this will depend on the legal framework applicable.