Yes you need to use the bolts, this is what gives you the extra strengh.
These are much stronger than other versions offered of this bracket infact when I bought your origional design i bought it not so much for the extra flex from angle correction ,but for the bracing of the shackle box ...And now these are even sweeter . The other folks design might be slighly easier to install ,but that's only b/c they skip on the frame tie in for lateral support ...I even was told that if you don't abuse the other folks design it should be fine...I'm not sure how you define abuse in an offroad situation since I can easily slip off a large boulder and side load the bracket with force , and this design would be the one I'd pick to hold up over "ROUGHER" designs ...lol