Ha! I never realized that, but you are correct, as per CCI 93325 is allowed with modifier. That is confusing. But the code description itself states 93306 includes all three components: 2D, Color-flow and Doppler.
If your physician is billing for an Echo, just a plain ole' Echo and he performs a complete echo as listed under 93306, then no, he should NOT be billing 93320/93325 in addition.
But you also have a Stress Echo. For a stress echo in the hospital you would bill: 93350. 93016, 93018 and 93320/93325, if performed.
Stress Echo in the office - 93351 (this code includes the stress portion), 93320/93325.
Personally, I do not think both of these should be billed. Did your physician do just a Echo or did he do a Stress Echo?
Per NCCI you can bill 93350/93306 with a modifier but your documentation will have to be solid and really illustrate medical necessity for both.
93350 93306 20090101 * 1
HTH