Hi Ethan, welcome to NST.
EasyBCD is not a boot manager or a boot loader. It's mainly a GUI for the Vista BCDedit command-line utility, with extra facilities for handling grub and interfacing with other tools.
Whether EasyBCD is installed or uninstalled makes no difference to the Vista bootmgr. It just makes life easier for you in maintaining your BCD.
Vista SP1 replaced the bootmgr module, but your problems with it might have been due to other factors.
Several people had problems because they rebooted when the install had an apparent hang at 99% complete. (It stopped communicating but it was still updating the system). The reboot caused an incomplete update leaving the system unusable.