In-service distribution on account of disablity

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The plan document allows for in-service distributions on account of disability. Disability is defined as the inability to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment that can be expected to result in death or which has lasted or can be expected to last for continuous period of not less than twelve months.

The participant has been on social security disability for about 12 years and works part-time (apparently making less than the amount which would affect his social security disability benefits). He has work for the company under this arrangement for about 15 years and is currently requesting an in-service disability withdrawal.

What I am having a problem with is the fact he is and has been employed for the last 15 years with this company. However, am I suppose to be reasoning that he is only able to work part-time and that his position cannot be defined as substantial gainful employment?

Assume he is entitled to an in-service disability distribution. Does the fact he is on social security disability automatically qualify him for the 10% waiver?