Was it wise for the versailles delegates not to allow other nations or ethnic-group representatives, such as ho chi minh or w. e.b. dubois, to speak at the conference?

NO it wasn't wise at all, it failed to achieve lasting peace, here is the reason why the war to end all wars weren't wise

The final days of the First World War were  gruesome and awful. The end of the fighting took place through an armistice which was signed in a railroad car in the French town of Compiègne. The armistice was not a peace treaty, only an agreement to stop the fighting in order for a formal peace treaty to be negotiated; It was obvious with the abdication of Kaiser Wilhelm II and the military situation in November, 1918, that the Germans had been defeated.
The cost of World War I, both in terms of total casualties as well as monetary costs was unbelievable.  The teacher may also wish to ask students to compare the number of civilian casualties. The "First World War By the Numbers" site, estimates the total number of civilian casualties to be approximately 8 million persons. Additionally, there were 10 million military casualties. Those numbers do not include the 20 million people who were wounded. The financial cost of the war was also staggering. To the U.S. alone, the war cost 32 billion dollars.