Well, as you no doubt recall, The Guide Mark II (introduced in Mostly Harmless) was a Vogon-engineered, bird-like, multi-dimensional, time-traveling WMD. If it is considered a legitimate version of the Guide, then no, the Guide was far more than an ebook/ereader. Trying to read it on your Kindle might prompt the Guide Mark II to turn your device into sentient radioactive slag that would kill your great-great-grandparents whilst simultaneously taunting your great-great-grandchildren, just for sport.
Even in the "Mark I" sense, I think the Guide was more like a combination of an iPad, Wikipedia, and Stack Exchange - evolving, dynamic, non-linear, and subject to various kinds of abuse.
So, my vote is: no, the Guide is neither ereader nor ebook, and trying to use it simply as either might cause justified panicking.