Nice article by Nick Hoffman and fairly well evenhanded.

However, Victor Baker and James Head are Mars scientists still supportive of an early ocean on Mars:

The Northwestern Slope Valleys Region, Mars: A Prime Target for the Future Exploration of Mars
*J M Dohm, J C Ferris, R C Anderson, V R Baker, T M Hare, W C Mahaney
http://www.agu.org/cgi-bin/wais?w=P71A-0446

Oceans on Mars: An Assessment of the Observational Evidence and Possible Fate
*M H CARR, J W Head
http://www.agu.org/cgi-bin/wais?w=P51B-0357

The Carr/Head report does suggest that this ocean might be ice covered but that's only assuming *present climate conditions* :

"Under present climatic conditions on Mars an ocean would freeze in a geologically short time period (~10**4 yrs), then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface. The present VBF is plausibly interpreted as a sublimation residue from the ponded outflow channel effluents."

But we know that almost certainly Mars climate does not stay constant for the same reasons that Earth's does not: because of obliquity changes and other orbital variations. At the most extreme angles of tilt, say at 60 degrees, the polar ice cap would largely melt and so would an ice cover of a northern ocean.
Note as well the lifetime of such an ocean is uncertain so it is conceivable that it could persist long enough for life to develop undersea, such as near hydrothermal vents for example, even if it were ice covered.

Bob Clark