do 6FTM blends often resemble each other--
If you're talking about the factory, yes. Most of their productions if not specified otherwise are from the same area of Lincang, Fengqing. The Fengqing and Daxue profile stand in contrast to the Bingdao/Bangdong profile. Yiwu is a terroir, whereas 6FTM is just an old-school factory. They do have productions from Yiwu, but none I've tasted. The word is that after '06 or so their productions have really fallen off. Dunno.
My attention has been most totally on their Lunar Series, though I do have an '04 tuo which bears a milder Fengqing signature. There are some Tulin productions with a similarly robust taste, though their material comes from Dali, Wuliang. You might look into their '07 T868. There is also a Fengqing TF, which has some famous productions and Mengku Rongshi is in the same area. I have an '06 from Daxueshan which is quite nice. The edges on their productions are considerably more refined than any of the aforementioned factories, which suits me best.
are other teas labeled as 6FTM sometimes connected to 6FTM factory (e.g. using a recipe made/inspired by them)?
6FTM is an official title conferred by a Qing Dynasty (1644-1911) magistrate in the 19th-c. It references the Yiwu terrior, Gedeng, Yibang, Yiwu Zhengshan and so on. It has no bearing on the factory, which is in Lincang, Fengqing. There are two v. distinct profiles from Lincang: baqi/aggressive and rouqi/genteel. Easily the most famous production from Lincang is Bingdao and next Xigui, if price is any indication. These are decidedly in the genteel category.