He is widely respected as a "moderate" Muslim leader. He has never attracted the attention of authorities, and why should he? He hasn't blown anything up, after all.
Yet Sultan has asked Tariq Ramadan to reconsider his call for the setting-aside of traditional Islamic penalties (stoning for adultery, amputation for theft, etc.). He seems to revere Qaradawi, who has justified suicide bombing and violent jihad, as an authority. But no one in America thinks of that sort of thing as any cause for concern.
"Columbus, Ohio Muslim Leader Says 9/11 Planned by Americans, Praises the Wanted Al-Qaeda-Linked Yemenite Sheikh Al-Zindani," from MEMRI, with thanks to all who sent this in:
Dr. Salah Sultan is president of the American Center for Islamic Research (ACIR), a non-profit organization registered in Ohio and located in Columbus. On his website, he asserts that the main purpose of the ACIR is to "serve Allah (God) in the best way possible through the principles laid out in the Quran and Sunnah," to address misconceptions and extremism, to build bridges with non-Muslims, and to provide fatwas. 
Dr. Sultan, who has been called "one of America's most noted Muslim scholars,"  is signatory to the Council on American-Islamic Relations (CAIR) 2005 fatwa against terrorism,  and is a former professor and president of the Islamic American University in Michigan.  He is president of the American Institute for Religious and Cultural Studies, and active in the European Council for Fatwa and Research (headed by Islamist sheikh Yousef Al-Qaradhawi  whom he calls "our great scholar"  );the Fiqh Council of North America; and the International Association of Muslim Scholars.  He previously served on the board of directors of Islamic American University, and on the Muslim American Society Board of Trustees.  Dr. Sultan's resume states that he also serves on the board of trustees of the International Union for Muslim Scholars, and is a member of the Council of Indian Scholars and of the Association of Scholars in Germany. 
There is a lot more to his resume at MEMRI, attesting to his influence in the American Muslim community.
According to his online resume, Sultan's "vision" is: "To live happily. To die as a martyr." 
On May 17, 2006, Dr. Sultan appeared on the Saudi Prince Walid bin Talal-owned Al-Risala TV channel.  In his appearance on Al-Risala TV, Dr. Sultan praised Yemenite sheikh Dr. Al-Zindani, who has been categorized by the U.S. government as a "Specially Designated Global Terrorist" because of his loyalty to Osama bin Laden and his support of Al-Qaeda.  According to the U.S. Department of the Treasury, Al-Zindani "has a long history of working with bin Laden, notably serving as one of his spiritual leaders. In this leadership capacity, he has been able to influence and support many terrorist causes, including actively recruiting for Al-Qaeda training camps." 
In March 2006, Al-Zindani appeared on Yemenite TV at a Hamas fundraiser.  TO VIEW THIS CLIP, VISIT: http://www.memritv.org/search.asp?ACT=S9&P1=1086.
The following are excerpts from Sultan's May 17, 2006 address on Al-Risala TV. TO VIEW THIS CLIP, VISIT: http://www.memritv.org/search.asp?ACT=S9&P1=1143.
Salah Sultan: "The film 'The Siege,' starring Denzel Washington, portrayed the Muslims in a very bad light. They are shown calling for prayer, performing the ablution, praying, and then planning multiple bombings - a government building, a security agency, the FBI, a bus carrying young men and women, adults and children. They bombed shops.
"The film came out in April 1999. It paved the way for 9/11, since it was filmed in Brooklyn, New York. The truth is that immediately after 9/11, I said people should view these events in the context of 'The Siege,' because these events were identical.
"This scenario... I still believe to this day... This scenario still baffles me. I share the view of many Americans, French, and Europeans, who say that 9/11 could not have been carried out entirely from outside [the U.S.] - by Muslims or others. The confessions by some people could have been edited. But even if they were not edited, I believe that these people were used in a marginal role. The entire thing was of a large scale and was planned within the U.S., in order to enable the U.S. to control and terrorize the entire world, and to get American society to agree to the war declared on terrorism - the definition of which has not yet been determined.
"The U.S. remains the only country to determine who is a terrorist, and what is the definition for terrorism, and it can pin it on anyone. The most recent instance is the case of Dr. Al-Zindani, who has been accused of terrorism, even though he is known worldwide for his refinement, virtue, and broad horizons."