From the research I know of, the GDR had a fairly significant role in the war through training and aid. Not surprisingly, it was the Stasi model that the Democratic Republic of Vietnam found most useful. The GDR provided organizational models, tactics for suppression of dissent, and even technical assistance with specific tasks (like copying the ID cards of South Vietnam). This was increasingly important into the 1960s when the DRV government had serious internal dissent among party members as the rift between the Giap-Ho Chi Minh (ideologically Soviet) and Le Duan-Le Duc Tho (ideologically Chinese) factions competed. The Le Duan side wins out and repressed the Soviet faction through various purges. One historian notes the irony that Soviet tactics, filtered through the GDR, were used to suppress Soviet trained Vietnamese. On weapons, he says that the DRV traded US weapons to the GDR so that they would study them. There's one specific article on the DRV-GDR security/intelligence relationship by Martin Grossheim. The GDR was also a leading opponent of the war, participating in the Soviet sponsored World Peace Council congresses. They certainly had a role in building the police state that still exists today in Vietnam.

Hopefully someone with more background in the military aspects can add something about weapons exchanges.