There is no contraindication for the use of Plan B while treating bacterial vaginosis.
It is important to note that some sources may list a contraindication, but it would be incorrect. Plan B contains a high dose of a common progestin, levonorgestrel. In addition to being used in many oral contraceptives, it is also the progestin used in contraceptive IUDs (intrauterine devices).
The use of IUDs is contraindicated in patients with untreated acute cervicitis or vaginitis (including bacterial vaginosis). Many online references simply list contraindications with all products that contain levonorgestrel and do not differentiate between different forms (e.g. oral or IUD).
The only absolute contraindication with use of Plan B is pregnancy.
In addition, topical creams for the treatment of bacterial vaginosis would not interact with Plan B, so there is no need to worry of drug interactions.