No, it definitely matters. Right now Luther Strange is holding Sessions' seat, and will continue to do so with voting rights until Jones is sworn in. Strange, while not a pedophilic rapist slavery apologist, is still a Republican. As such, the Senate is currently 52-48 in favor of the Republicans. This leaves room for three dissenters, as Mike Pence will tiebreak in favor of the Republicans at 50-50 unless he gets all backstabby all of a sudden, and I don't think a man who surrenders his fraternity's kegs to the police is all that into intrigue.
Once Jones is in place that will become 51-49, leaving room for only two dissenters.
Presently, the likely Republican dissent is composed of two centrists (Collins and Murkowski), the far-right under Rand Paul and Ted Cruz, and the "Last Chance Caucus" (Corker, Flake, and McCain).
The tax bill specifically is more opposed by the centrists than anything else, though Rand Paul continues to whine about not literally disestablishing the IRS and repealing the Seventeenth Amendment and the current Senate bill contains the skinny repeal that McCain rejected. The senate including dissenters already passed this version of the bill, though that is not necessarily indicative of the dissent pattern since the main reason for passing it is to have a proposal for the House to negotiate with.
In my mind the tax bill's main opponent is currently time, not Jones getting seated. They are rushing through a piece of major and mostly unwritten legislation with the end of the session upcoming. Much like from your shitty cousins you never see, we might get a very terrible Christmas gift indeed, even worse than a well-written right-wing gift to the rich by way of being badly written.
God only knows what the doner class thinks of these proceedings. Obamacare repeal failure, Democratic sweep back in November, Jones winning, and now the tax bill is a shitshow.