Drive 4 DC motors off a dual drive motor controller
Since nobody better qualified has answered, I'll take a crack at this one.

Simply looking at the current draw, it looks OK.  But it's close enough that you might want to verify the current draw just in case the motor makers took a little "creative license" with the specs.  Check the current under both no load and max load.

But, what I would be most concerned with is the speed of the motors.  It's almost certain that two motors will not be matched in speed.  And even if they are, they won't stay that way due to age, wear, and differences in weight distribution and terrain. 

This difference in speed, especially with a geared motor that won't tend to slip, will manifest itself as stearing problems, increased wear on the wheels, and other bad things.

But, assuming that the current spec is correct, I don't see any harm in just trying it.  There is a chance that I'm wrong and they will be matched enough that it'll work just fine.