In ODIs yes, but they did play a 50-over match at the 2005 ICC Trophy, which The Netherlands won by shitloads.If I stand to be corrected Oman playing Netherlands in an ODI will be a 1st time these teams have ever played each other.
NED vs OMA Cricket Scorecard at Carrickfergus, July 02, 2005
Live Cricket Scoreboard: Get Netherlands vs Oman cricket scorecard, ICC Trophy 2005 dated July 02, 2005.
www.espncricinfo.com
Oman had only been an affiliate member of the ICC for five years at that point, and didn't get to associate status until 2014.
They have also played a bunch of T20Is, including in the 2016 T20 World Cup, and some T20s that didn't have full T20I status.