A positive displacement pump will increase pressure to maintain the volumetric flow if you backpressure it. That isn't great for life to deadhead it. You want to keep it at low pressure.

I sent some questions to the mfgr as I was curious. They responded with some very useful info. I'd be thinking about his advice on moisture control and rebuild intervals.

The piston pump is a good choice for pond aeration. The 2668 is a two
headed pump with an integral manifold that connects the two heads in
parallel. On the attached drawing you'll see there is one inlet connection
(that allows incoming air to enter both heads at the same time, and one
discharge connection. Therefore, we are adding the flow each head
together. You could 'T' into the discharge line for a pressure gauge.

This pump is rated for continuous duty and can run 24/7. Pump life depends
a lot on the operating pressure and pump operating temperature. The higher
the discharge pressure, the more pressure is placed on the piston seal
forcing it against the cylinder and creating more friction. Also, the
higher discharge pressures create higher operating temperatures. The
installation must have as much cooling air as possible - the cooler the
pump runs, the longer the piston cup will last.

The piston cup is the main wear item. It is a Teflon impregnated compound.
I would expect at least a years worth of running continuous in a good
installation, and as much as 3 years in the right conditions. I would plan
on a rebuild once a year, but monitor how the pump does to see if you can
stretch this. One other note of caution - piston pumps do not handle
moisture at all. If any liquid gets into the pump, the piston seal can
wear out in a matter of days. Please make sure to mount the pump so that
the discharge line is piped down so that when/if the pump stops and
condensation occurs due to cooling, it will not flow back into the pump.
You may want to consider a discharge check valve to prevent any backflow.

I would suggest a tube ID of no less than the discharge port size (1/4"),
and certainly stepping up to 3/8" or 1/2" will reduce pressure drop, but
not significantly at this low flow.

Your other choices for pumps would be a rotary vane or a diaphragm pump.
These tend to be more expensive and don't offer any advantage from a life
standpoint. However, the diaphragm pump can handle moisture better than
any of the other two.