You can only claim a non-relative as a dependent under the Qualifying Relative rules if they meet all the requirements. The main requirements are that they lived in your home as a member of your household for the entire year. That they had gross income of less than $4,050 (Social Security does not count). And that you provided over one-half of their support. Since he had income from Workman's Compensation and Disability payments you will need to use this IRS worksheet to determine support - https://apps.irs.gov/app/vita/content/globalmedia/teacher/worksheet_for_determining_support_4012.pdf
To be a Qualifying Relative -
1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross income for the year must be less than $4,050 (social security does not count) in 2017
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen or a U.S., Canada, or Mexico resident for some part of the year.
6. The person must not file a joint return with their spouse.
Social security doesn't count as income, for the income test, nor does workman's compensation or non-taxable disability income*. But that money he spends on himself does count as support not provided by you, for the support test.
*Not all disability income is tax free. If he receives a W-2 (with an amount in box 1) or 1099-R, the income is considered taxable.