Assuming Pelosi is Speaker, how would it affect the January 6th count if she refused to seat the Reps who plan on objecting to the electoral votes?
There would be no effect, because Speaker Pelosi cannot refuse to seat a duly-elected candidate.
When Can Congress Refuse to Seat a Duly-Elected Candidate?
In 1969, the U.S. Supreme Court ruled that the Speaker of the House could not exclude a duly-elected candidate for the U.S. House of Representatives.
Once seated, the House could vote to expel the member by a two-thirds vote.
While Pascrell may wish to exclude some representatives, a mistake appears to have been made in the analysis of the authority to exclude those members.
In Pascrell's letter to Speaker Pelosi, Pascrell quotes a Congressional Research Service (CRS) report, Expulsion of Members of Congress: Legal Authority and Historical Practice, January 11, 2018,
Consequently, I call on you to exercise the power of your offices to evaluate steps you can take to address these constitutional violations this Congress and, if possible, refuse to seat in the 117th Congress any Members-elect seeking to make Donald Trump an unelected dictator.5
5The Supreme Court in Powell v. McCormack acknowledged Congress “may exclude a Member-elect with a simple majority.” See https://fas.org/sgp/crs/misc/R45078.pdf;. (The Court found restrictions on Congress’s exclusionary power, but had restrictions existed in 1861, the seating of treasonous members-elect in the 37th Congress would have spelled the end of the nation. 395 U.S. 486, 547-48 (1969). The ruling also does not assess Amendment 14, Section 3 (which was enshrined to exclude seditious Members-elect), as petitioner Powell was not excluded on those constitutional grounds.).
The CRS report does say,
Unlike the two-thirds majority requirement of the expulsion power, a body of Congress may exclude a Member-elect with a simple majority.6
6 Id. [Referring to Powell v. McCormack, 395 U.S. 486, 492-32 (1969).]
However, later, referring to Powell, the report notes limits to the authority to exclude.
While the Court recognized that the Constitution grants broad authority to each of the houses of Congress regarding expulsion and other discipline, it explained that Congress’s authority regarding exclusion was limited to the enumerated qualifications requirements.14
14Powell, 395 U.S. at 522 (“[T]he Constitution leaves the House without authority to exclude any person, duly elected by his constituents, who meets all the requirements for membership expressly prescribed in the Constitution.”).
The enumerated qualifications are given in Article I, Section 2, Clause 2: Qualifications of Members of the House of Representatives
No Person shall be a Representative who shall not have attained to the Age of twenty five Years, and been seven Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State in which he shall be chosen.
Thus Pascrell plan to exclude some representatives has no chance at all.