Getting a pub or not will depend largely on you, your mentor, your project, and where the project is when you arrive and when you leave.
In terms of being at the NIH, the networking opportunities are terrific. I had an offer for a post bacc fellowship before I left at the end of the summer after my Junior year. Labs are very different from university labs, and, in my experience, the lab I was at was way more productive. Mostly because most of the research was done by post docs as opposed to grad students and a full time lab manager ensured that we had everything we needed for our experiments all of the time and also made sure the lab stayed organized and tidy.
For me personally I found it very beneficial to meet a lot of MD/PhD researchers doing post docs/fellowships or running labs at the NIH. I had several long conversations with the ones in my lab and others at the NIH (which I set up by email) and these helped me solidify in my mind that the dual degree path was better for me as well as giving me a more concrete picture of what the end of training / job outcomes looked like.
10/10 would recommend.