Yes, the FAA prohibits any -121 (airlines like Delta, UAL, etc.) from flying a circling approach (in IMC WX mins). They are the most dangerous type of "normal" flight operation, so they are not allowed.
If you have the weather minimums, you are allowed to descend on an instrument approach until you reach VMC, and then fly a normal visual traffic pattern and approach. The WX mins, in the US, for a visual traffic pattern are much higher than for a circling approach.
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