I would not recommend it. If you did, you could / would probably / get some of the water
that is pumped by one pump
run back through the other one. You could prevent this with a check valve on each pump
, or slightly less effectively by a loop in each live before the 'Y' valve... but neither solution is ideal.
I would recommend going ahead and adding a second discharge throughhull.
For some other considerations to think about you may want to take a look at this; Bilge Pumps, employment, care and feeding.
You will see my (some say overkill) dewatering set up if you are interested.