You can believe what you want if it helps you sleep better at night. Basically all lineage masters practiced karmamudra. Guru Rinpoche, Mandarava, Yeshe Tsogyal, etc., Tilopa, Naropa, Marpa, Milarepa, Gompopa, Phagmo Drupa, etc., It's hard to find anyone responsible for the existence of Tibetan Buddhism in Tibet who did not practice karmamudra. Karmamudra is part and parcel of buddhist tantra. But that does't mean you have to practice it. There is karmamudra, samayamudra, dharmamudra and mahamudra. One can rest in the nature of the vajra, as in mahamudra, or join feeling to mahamudra as in tummo, or visualize consort as in deity yoga, or for those practitioner who require a basic concrete viceral introduction to the practice, then karmamudra. Actually, karmamudra is taught as a low level practitioner's tool.The highest capacity practitioners are introduced directly to mahamudra, and so on, in descending order. But, also even for high level practitioners, if they have difficulty bringing all five vayus into the central channel, then karmamudra will be employed. As in the case of Milarepa, this event happens to someone on the doorstep to buddhahood. Such a person is extremely advanced practitioner. And in such a case, dakinis and celestial beings can serve as the consort.
Thanks for the post. After reading the article of Ocean of indivisble method and wisdom by Geshe Acharya Thubten Loden, I have come to realize that the union is actually symbolic and has nothing to do with sex (as attachment of sensual pleasure) but rather a necessary process for these advanced practitioners (who have detached from attachments) to realize enlightenment...So I am not entirely not correct.