Let's set the record straight.  There is no union, ever, that should object to an employer who wants to pay a union member more, or treat them better, or even reimburse over and above than what's expected.  Collective bargaining agreements establish minimum standards.  Below is an excerpt from your Agreement that is extremely clear when it comes to recruitment.  This is a departmental decision.  The HOA bargained for your department to have this flexibility.  

In addition to the House Officer salary and payment to encourage savings, an individual House Officer may be granted discretionary supplemental payments, rewards or reimbursement by their department. Such payments may be used as recognition of a House Officer's professional growth and development and/or contribution in supporting the University of Michigan Health System's goals and interests. This may be used for recruitment to faculty positions.

As an example, all House Officers who were eligible for the $1,500 COVID bonus, received it.  Why?  Because the HOA contract allowed for a discretionary supplemental payment.