How has history viewed the presidency of Taylor?
The line was almost definitely intended to mention one of the caretaker Presidents, as the Simpsons put it^1, giving Tracy Morgan's character another niche and obtuse factoid to spout during the episode.
One of the most famous rankings of historical presidents, meaning before we have Gallup data, was done by historian Arthur M. Schlesinger. Schlesinger, and later his son, conducted several surveys between 1948 and 1996 asking relevant historians to rank presidents according to a field of criteria. For the 1948 poll, which has garnered the most attention, participants were asked to decide the ranking of each American president according to seven criteria. They were^2:
1.) The general prestige applied to the President at the present time (High/Low)
2.) The strength of the role the President played in directing the government and shaping the events of his day. (Strong/Weak)
3.) The approach taken by each President toward his administration. (Active/Passive)
4.) An evaluation of the idealistic or practical nature of the official actions of each President.
5.) An evaluation of the flexibility or inflexibility of the approach each President took in implementing his programmes or policies.
6.) An evaluation of the significance attached by each of the respondents to the accomplishments of each President. (Great/Little)
7.) An indication of the amount of information each respondent possessed about each President. (Great Deal/Very Little)
This data was then compiled by Schlesinger and published in Life Magazine. In the two rankings done by Schlesinger, Taylor comes in at 25 out of 29^3 (1948) and 24 out of 31^4 (1963). Both of these rankings firmly put Zachary Taylor in the "Below Average" category of Schlesinger's ratings, however only his ranking in 1948 would qualify him as "One of the Worst Presidents of All Time."
Granted, these are expert opinions, and Tracy Jordan is a layperson. However, given that the character was born in the mid 1960s, recieved (and dropped out of) his high school education in the late 70s, and was commenting on Presidential legacies in the 2000s, it is safe to say Zachary Taylor was "generally" considered among the ranks of Harding or Hoover for Tracy Jordan.
Bibliography
https://books.google.com/books?id=ekoEAAAAMBAJ&pg=PA65&source=gbs_toc_r&cad=2#v=onepage&q&f=false
https://www.nytimes.com/1962/07/29/archives/our-presidents-a-rating-by-75-historians-a-poll-of-exports.html?url=http%3A%2F%2Ftimesmachine.nytimes.com%2Ftimesmachine%2F1962%2F07%2F29%2F356745922.html (Hidden behind a paywall, sadly. If asked, I can provide an accessible version, but this is to prove I'm not pulling the numbers out of my ass.)