Teams over the luxury tax threshold usually don't make that kind of gambles. They're too expensive.
Are there any provisions in basketball about minimum contracts and the cap?
The minimum salary is different for each player depending upon their years of service time. This season, the rookie minimum is $442,114, whereas the minimum for a ten year vet is $1,262,275. Despite that, if a team signs a veteran with 2+ years experience to the roster, they are only responsible for the salary obligation for a 2-year veteran's minimum, which this year is $797,581. The league pays the rest.
That's not as clear as I'd like it to be, so let me use an example:
The team signs Alonzo Mourning. As a 10+ year vet, he earns $1,262,275. However, of that amount, the Celtics are only responsible for the first $797,581. This is also the amount that counts against their salary cap and the luxury tax. The NBA itself then chips in the remaining $464,694 to Mourning.