Spikes are 'in the blood' -- if you take Kraxis blood, you get a Spikes of Kraxis, regardless of if you take defensive. Defensive won't give you a starting unit change.
I think some of the other bloods give similar (Najaborn for Urxen - poison vial given).
It would be nice if the militia was converted for a few bloods though. Right now I've only seen the spear unit modfied.