in New mexico does a conditional waiver become unconditional once the check has been cashed

Yes, a conditional waiver will become fully binding (i.e. waive lien rights) once payment has been made. Deposit of payment is the "condition" that must be met in order a conditional waiver to be enforceable. Also, since New Mexico doesn't regulate the form and content of lien waivers, review the terms carefully to be sure that the waiver is indeed conditional and that you aren't waiving more than just lien rights. 

For more information, see:

• Conditional vs. Unconditional Lien Waivers 
• The Ultimate Guide to Lien Waivers