Welcome to GMT Nation...
In the GM Factory OEM "Keyless Entry" Setup... The BCM and LGM are intimately co-involved. However, in this Self-Contained "Plug-N-Play" sort of design in the After-Market Products... as shown in both Videos... they seem to not need to get involved with the BCM in any way, shape or form. YMMV from Other Member Suggestions.
@Stuntmanmike77... Regarding whether or not these types of installations are considered for "DIY" work...it would depend on whether you have some decent skills with Basic Electrical Wiring and Wire-Electronic Schematics Reading ability... as well as having the -=Stones=- (8) to mess around with their Equipment and arcane Instruction. What often seems simple and straightforward on paper...can easily descend into the Hell of "Wire Spaghetti Soup" if things are not where thay are supposed to be 'Down in the Basement' under your Dashboard and cooperate with you.
As for which type and selection of Keyless Entry-Remote Start "Plug-N-Play" Hardware to Choose from and BUY... Scour eBay and Amazon as well as making a Google Search or Two on the topics of the "Best Plug and Play Remote Start Up System for Trailblazers and Envoys" and see what *Pops* 8>)