My brother is infirm and has a DTC certificate on file with CRA. I am claiming him as my dependent. he receive ODB. is that considered his net income?

You will need to do a tax return for your brother first, claiming the income and using his personal credits first.  Often disability pensions are none taxable.  Once his return is complete, you can then transfer the remainder to you.  You cannot simply claim him as a dependant, enter his income, and then use the DTC.  It has to be transferred to you.