Whilst there are already correct answers I thought I would add some further illustration:
A Google search for "plastic glasses" (with the quote marks) returns almost a million results. Of the top results returned, a large selection are from retailers selling "plastic glasses".
Your question title asks if the term is valid for a container. The answer is absolutely yes.
In British English it is very common; I will defer to an American friend to clarify its usage in the States.
Here, in the Manchester Evening News, the term plastic glasses is used as you would expect.
Police are advising pubs and clubs to use plastic glasses and employ extra door staff for Monday night’s crunch Manchester derby.
The term has also been used here by the BBC:
A proposal to extend the use of plastic drinks glasses to all pubs in the Highlands has been dropped.
As I mentioned in an earlier comment, the term plastic glasses is used regularly at concerts and sporting events.
You may well have asked for a glass of wine at the rock gig but you wouldn't be surprised if it was served in a plastic vessel of some description.