you've slightly misinterepted the 3dmaths commands - understandable as I think your way possiably makes a bit more sense
Using the dgdk you do not store your own vectors and matrices etc, you ask dgdk to create them and it stores them for you internally and provides you with commands to retrive values from them. When the 3d maths commands ask for a vector parameter they mean the integer identifier for the vector stored inside dgdk - just like how the object commands need an object id see? its the same thing. Your code would read something like this:
dbMakeVector3(1); //create a vector with id of 1, same as your v_Test
dbMakeVector3(2); //create second vector to store the look vector of your object
dbSetVector3(1, 0.0f, 0.0f, 1.0f); //set the values in vector 1 to the same as you had above (except floats)
dbSetVector3(2, vlX, vlY, vlZ); //assume you have the look vector stored in these variables, you can retrive the look vector as you did originally
float fDot = dbDotProductVector3(1, 2); //get the dot product between vector 1 and 2
I hope that helped
