No. some functions do not work. this comes because in vvvv we use Xpath only for retrieving the VALUES of selected elements. However, since i am currently reworking the XPath Nodes anyways, i will also have a look on which functions might make sense to implement.
I can already say for the next vvvv release: Xpath (XML) will become XPath (XML Get) with litte changes. per default you will always get the xml data of the elements of the selected nodes unless you dont use the text() function, which will return the VALUE of the selected node. also the XML Input document will be spreadable.
Beside that there will be a node XPath (XML Set) which will be able to set specific Values of selected XML Elements.
Anyhow. for the specific use of the count() funtion i patched a workaround which does the same for you.