There is not a Theravadin temple or center in my immediate area. The nearest ones are hours away. In support of my practice, I'm active in both a Gelug Dharma center and a lay Soto Zen sitting group. The Dharma center has a resident Geshe providing excellent teachings, but I'm not really into all the ritual. So I go to classes and consult with Geshela when needed, but don't participate in most religious services. Every one seems cool with that, including Geshela. I sit with the Soto Zen group because I find group meditation sessions provides a great deal of support to my practice, I really admire the focus on practice, and the ritual is at a minimum (a few bows and chanting the Heart Sutra). Once again, every one seems cool with me preferring the Theravada.
As far as the difference between meditation techniques, who, besides yourself, is going to know you are doing vipassana as opposed to shikantaza?