Does the ACA require "seamless" access to contraception?

No. That phrase came from Judge Pillard's opinion in Priests for Life.

At several points during oral arguments in Little Sisters of the Poor v. Pennsylvania, Justice Ginsburg stated that the ACA requires "seamless" coverage of contraception.

JUSTICE GINSBURG: The glaring feature of what the government has done in expanding this exemption is to toss to the winds entirely Congress's instruction that women need and shall have seamless, no-cost, comprehensive coverage. Seamless, no-cost, comprehensive coverage….

And I just wonder if I --if there is no substantial burden, how can the government justify an exemption that deprives those women of seamless coverage? …

JUSTICE GINSBURG: I would ask Mr. Clement the same question I asked the government. The --at the end of the day, the government is throwing to the wind the women's entitlement to seamless, no cost to them.

The word "seamless" does not appear anywhere in the ACA. (Indeed, the ACA makes no mention whatsoever to contraception.) The Obama administration adopted that phrase from Judge Pillard's decision in Priests for Life v. HHS (2014).

"The accommodation is the least restrictive method of ensuring that women continue to receive contraceptive coverage in a seamless manner while simultaneously relieving the eligible organizations of any obligation to provide such coverage."

Then-Judge Kavanaugh dissented in that case. (See pp. 509 of Unraveled.) 

Later in the arguments, Clement explained that the demand for "seamless" coverage made a resolution impossible:

MR. CLEMENT: I –Mr. Chief Justice, in the wake of the Zubik remand order, there was a lot of back and forth between the religious objector –objectors and the government, and I don't think that there really was a mechanism to find sort of some third way because the government has always insisted on seamless coverage, with seamless, essentially, being a synonym through –for through the Little Sisters' plans.

So long as supporters of the mandate demand "seamless" coverage, there really is no way to work out this conflict. Clement made this point:

Clement: I don't think that there really was a mechanism to find sort of some third way because the government has always insisted on seamless coverage, with seamless, essentially, being a synonym through --for through the Little Sisters' plans.

That argument works with another employer who does not use a church plan.