Probably.
From Roberts, "Although variceal rupture has occurred during insertion of instruments into the esophagus, several studies suggest that NG tube passage is generally safe, even in the presence of esophageal varices."
Emedicine suggests that history of varices is a relative contraindication to NG lavage.
Bottom line: Probably safe but don't do the procedure if not absolutely necessary.
Sources
Roberts: Clinical Procedures in Emergency Medicine, 4th ed.
Shlamovitz, G. MD and Shah, N. MD "Nasogastric Tube" Emedicine. http://emedicine.medscape.com/article/80925-overview. 20 June 2008.