no not at the moment, oslo.master page is related to the classic site.
any default master page and/or custom styling will not be reflected on modern pages.
Modern pages and sites/libraries use a different master page that is inherited from a team site only at the moment. When they bring out publishing site then you can update the master page if Microsoft will allows it.
right from the horses mouth:
These customizations are currently not supported for "modern" pages:+
Adding "classic" web parts on "modern" pages
Custom CSS via AlternateCSSUrl web property
SharePoint Framework Extensions)
Custom master pages (more extensive branding will be supported later
using alternative options)
Minimal Download Strategy (MDS)
it is best practice to not mix the two. Leads to bad user experience and continuity.
best you can do on a modern site is to switch off the quick launch:
top left click on the cog icon -> click site settings -> under Look and Feel click on "navigation elements" -> uncheck "Enable Quick Launch" and click ok.