I'll try my best to make it the easiest to understand!
-When fluid intake is low or the concentration of solutes in the blood is high, ADH is released from the pituitary, more water is reabsorbed, and less urine is excreted.
*Just think: The water is reabsorbed to equal out the concentrations in the blood. Therefore, this water won't be included in the urine output. So yes, in Fluid Volume Defecit, ADH will be stimulated and would cause the reabsorption of water, which in turn increases the volume of fluid in the body.
Hemoglobin- the red pigment in red blood cells that carries oxygen
Hematocrit- the proportion of RBC to the total blood volume
(the amount of red blood "cells" in relation to the plasma it's carried in)
Hope that helps!!
If anyone sees an error, PLEASE correct me!