Is he good at business? Yes. Is some great businessman that you should look to for advice on how to run a long lasting company? No. He has made some good real estate decisions and overall has a good record in the construction field, but most of his companies are high risk areas. Things like hotels and casinos are great if you are after a quick return on your investment but generally not good for steady long term growth. They are also highly prone to fail at some point. That allows you to make some good money in a short period of time, but it also means there is a good chance that your business is going to fail.
Trump is very good at branding though and has gotten a number of people to want his name plastered on their building, as it is a good draw to the public. Overall though his experience is in short term businesses and not long term businesses so he could likely offer some good advice on how to make a few million in a fairly short period of time. If though you are looking to make a business that you could pass on down to future generations and it remain steady and profitable, you would be better off talking to someone like people who started Walmart or IBM.
People have a tendency to equate being smart and experienced in a specific are with being smart in the overall broad dept. People also take how smart a person is by how well he talks. Some of the smartest people in history have not been the most articulate speakers and some of the greatest leaders in history have not been the person with 5 PHDs.