Roppongi is pretty much safe, specially during daytime, just like the rest of Japan. There is an issue during night time however, just like Kabukicho (where I think it's actually worse, but I have been there only once): When you walk around those two areas, specially on the streets north and south of Roppongi crossing, you will see a lot of African immigrants advertising for night clubs.
A short disclaimer here, since I have been called sexist and been down-voted for reporting my experiences in Japan before: I have LIVED near this place for several years (It's a typical place for expats). And I have been in this area several times a year since 2001. During daytime and nighttime. I have been addressed by these people each and every time and I have never been addressed by anyone else than African immigrants. I am not racist. I am not judging. I am not storytelling. I am reporting facts from extensive experience, instead of changing reality to adjust to someone's sense for political or cultural correctness.
Bar touts, who have been subject to multiple complaints and even attempts to create rules on how someone can advertise for a venue, try to get you into red-light bars of different levels of seediness. Going into these can be always considered a certain danger, although considering the amount of people visiting them and the little amount of crime reported, I would still think that the overall crime level is very low. On the other hand, just like this also happens in Hong Kong, there might be a dark figure of unreported crime.
My take on the whole thing is this: You are still, at any level, much, much safer in Roppongi at midnight than many other places in the world during lunchtime, and on top of this on an exponential level safer than in any red light/entertainment area in the world. The question you have to ask yourself is this: If you were anywhere in the world, and you walk through an area at night, and a guy addresses you with "How about a Gentlemen's bar?", would you follow him?
If, however, you follow one of these guys into one of the night clubs and spend a lot of money there, or even give the impression of having a lot of money, there is a certain (but still low) risk that you will be a victim of theft or even worse. If you search for "crime Roppongi" on the web, you will see that most of the crime is either Yakuza-related which generally does not affect foreigners, the others are a few incidents that spread to dates back in 2004. You will find more hits if you search for "roppongi africans" because people complain.
So the harassment is the much bigger issue. There are certain methods to avoid trouble or harassment in this area, since the people who try to pull you into the clubs can be quite persistent. They are not allowed to advertise too far away from the place they are working for, but they might walk after you or even grab you by the arm. So here is my method to be left alone as much as possible:
Normally they are talking to people in suits that look like that might be able to afford something. If you look more like a backpacker, they do not care about you. They are looking for undecided people who do not know where to go and who can be convinced to go to a "Gentleman's club". The slower you walk, and the more you are browsing around, the more they will bother you. Knowing your destination, walking fast and looking straight ahead is the first thing you should do. If they talk to you, tell them "I am fine, thanks!" in a friendly, but determined voice. If they become persistent, tell them "You are wasting your time".
And as the quote you cited says: There are foreign national females involved. While I by no means want to say that you are 100% safe with locals, the chances that a local person knows enough English to drag you into something is pretty much zero. There are enough Japanese victims around for Japanese local crooks. If you are being addressed by a Japanese woman, chances are much higher that they want to get some free drinks or even marry a foreigner. It seems however that since the 2008 recession the expectations there to find a rich banker has converted into finding an IT specialist.
So this item you mentioned is pretty much local in Roppongi and Kabukicho in Tokyo. Other cities in Japan (Osaka, Kyoto, Sapporo) do not have this problem. Safety in Japan is very very high and it's rather this general safety that makes people overly careless. When I went to Japan the first time more than 20 years ago I had a shoulder bag that I carried all my cash, passport and return ticket with me. It had a small padlock. People made fun of me. In 2003 I once forgot my wallet in a taxi on the way to the hotel. The taxi driver showed up 1 hour later at the hotel lobby to bring back the wallet. It was more embarrassing for me for making the taxi driver come all the way back to the hotel. Of course he did not want to have a reward. Even more embarrassing for me.