Can Latex inner tubes be patched?
It is possible to fix both latex intertubes for clincher tyres and latex inner tubes inside tubular tyres. 

Whether you'll be able to do it, depends on your ability to do it. 

As you suggest, using a patch made from another latex tube and glue will work. This webpage suggests using tubular rim glue instead of normal patch glue for better results. 

That webpage also gives detailed instructions on how to mend a punctured tubular tire.