I both agree and disagree, Yudron. How's that for equivocation?
Listen, Kagyupas practice so-called "Sarma" deity practices, and also "terma" (Nyingma) practices, as a matter of course. We Karma Kagyupas like the Chogling Tersar, Konchok Chidu, and of course Yongay Mingyur Dorje's Termas have become a central part of our lineage, along with the Sarma practices of Phagmo, Demchok, etc. The details DO differ, as to how deities are generated, and their nature, etc., etc. No doubt about it. But I think it's possible to learn more than one way, and to understand there are a variety of methods, that complement each other, and "tease out" meaning, but I think these methods shouldn't be mixed. I'm pretty sure all lineages equate the Yidam deity with the Guru, at some level, as well.
On the other hand, I think trying to practice too many sadhanas at once is probably not a good idea for householders like ourselves. One approach is to incorporate all three roots into one practice. Another approach is practice three sadhanas, for each of the roots, and often various systems will combine these anyway. Another point to be made, is that some Lamas recommend a daily practice that incorporates all levels of Tantra--and there are methods to accommodate this within a single sadhana.
It's a huge topic, actually, and maybe not one for too much public discussion, now that I think about it. Which may have been your main point, after all!