The root cause for this scheme seems to be that the plan lacks cash available to give to the participant to make the loan. If so, then the scenario should start with the business making a cash contribution the plan sufficient to cover the MRC which would put the plan in the position to issue a loan check. That would provide a documented trail of the sequence of events.
The idea of writing a check to himself is a stretch in an attempt to circumvent the lack of availability of cash in the plan. This supposes that there is $50,000 in the business checking account (for the contribution) that would cover a check to his personal bank account (for the loan). If there are not separate checking accounts, would a bank even cash a check from an account payable to the account upon which it is written? If the bank will not honor the check, is it a valid financial transaction?
Trying to net the contribution and loan into a single transaction is vulnerable to an interpretation of events, and the IRS likely will have its own view of what transpired. Consider that the IRS could view the result of the net transaction as if the business funded the contribution by the having participant give the plan a promissory loan note secured by his vested balance in the plan, and then consider the potential consequences.
@Lou S.'s suggestion to have a clear paper trail is on point. If the plan has the cash to make the loan, the paper trail should methodically step through the participant takes the loan, the participant makes the proceeds of the loan available to the business, and the business funds the MRC.
If the plan does not have the cash to make the loan, the paper trail should include methodically step through the business funds the MRC, the participant takes the loan, and if necessary, the participant makes the proceeds of the loan available to the business.
This is not advice of an kind, nor a recommendation.
Frankly, this whole scenario has a whiff of a business in trouble and possibly with a plan that it cannot afford. Prudence would add taking steps to evaluate how assure the business and the plan can function within common norms.