Use of private OIDs in WG (standard-track) documents

Hello IETF,

small question: is it allowed to use private OIDs (i.e., subtree of 
1.3.6.1.4.1.XXXX.) in WG documents that are on standard track ? I am 
asking because in the TRANS wg, that is what is happening and I do not 
really feel comfortable adopting OIDs that are under the control of a 
single organization. Would this be a first case ?
Thanks,
Max