No, Nevel from iCarly and Robbie from the TV show Drake & Josh are not the same person. Reed Alexander has played the character of Nevel Papperman on iCarly since 2007, and the character of Robbie Bernstein on Drake & Josh was played by actor Ryan Alvarez from 2004 to 2005.
Ryan Alvarez has, however, appeared on iCarly before (but not as Nevel). Alvarez had a bit part (credited as "Employee") in the Season 3 episode "iCook" (episode 2), where Carly and Sam take on a TV chef in competition. The episode aired on September 19th, 2009.
Alexander appeared on hit television series Will & Grace in 2005 & 2006 in the recurring role of Jordan "Jordy" Truman, a relative of Will's. Very interested in politics, he attended the January 2009 Presidential Youth Inaugural Conference in Washington, DC, and also the inauguration itself. He has also done quite a bit of youth volunteer work for the American Cancer Society.
Alvarez has made many guest appearances on popular TV shows over the years, including It's Always Sunny in Philadelphia (2005), CSI: Crime Scene Investigation (2005), Monk (2007), and Ghost Whisperer (2010). Most recently he's appeared twice (2011 & 2012) as a quartet member on Victorious.
The sixth and final season of iCarly is currently being aired on Nickelodeon here in the fall of 2012, with the series finale scheduled to air in November. Star Miranda Cosgrove and the rest of the cast filmed their last episode in June 2012.