It will grow even if you plant it as a solid clump. Spreading it out more by the methods suggested just allows the carpet to fill in more quickly and evenly. After being in the tank for a couple of days you will see lines of new leaves popping up in the surrounding substrate.
DHG is a quick growing plant and likes a bit more CO2 and nutrients (possibly light also, although I wouldn't call it a high light plant) than your typical crypts etc. although they certainly benefit from nutrients also.
Nutrafin Plant Gro will not provide your plants with enough nutrients. It is more of a trace additive for elements your plants need in tiny amounts (iron, copper, etc).