Thank you for your question. There are various aspects of your question. I assume your question refers to the use of Agrobacterium rhizogenes by scientists to intentionally transfer genes from the bacterium to plants. Infection and DNA transfer from this bacterium occurs in nature all the time to cause disease. Such transformed plants are not classified as GMOs since transfer occurred naturally. If this is done by scientists then it would be classified as a GMO. Rules and regulations about GMOs are covered by the USDA, FDA and EPA. An overview can be found here. Each agency has its own set of particular rules and regulations, but all regulations deal with the insertion of foreign DNA by man. The foreign DNA can be of any source and would include vector sequences from Agrobacterium rhizogenes, Agrobacterium tumerfaciens or any other vector.
Your question reminds me of the recent finding that sweet potato was naturally transformed by the T-DNA from Agrobacterium tumerfaciens early in its evolution. Hence, the sweet potatoes we eat are as “transgenic” as the BT and round-up corn and soybeans we have, yet the sweet potato is not considered a GMO. This example points out the contradictory way we approach GM foods today.