Yes.
Looking at the battery specs, it is a 3.6V, 3.1Ah, 45.5g cell.
Cylindrical type | Lithium Ion Batteries | Batteries, Power supplies | Panasonic Industrial Solutions Global
Given the rumored ~8000 cells for the 300 mile Model S, this works out to
89kWh. The Roadster gets 236 miles EPA combined on 53kWh and would be rated at
396 miles on 89kWh. So on the Model S, it should be reasonable to expect to top 300 miles on this kind of pack.
As for weight, it works out to
364kg/802.5lb for the cells. The Roadster cells (6831 of them) seem to be 3.6V, 2.15Ah, 44g cells, working out to 300.5kg/662.3lb. The cell weight increase would be
63.5kg/140.2lb, which isn't too bad for so much more capacity.
Everything seems lined up for them to hit their 300 mile target.