Good question Liz...never heard of 2 pumps running on a single service line or at least for a hobbyist operation. I'm sure higher volume mega operations may just do so.
Just my thought...you could "T" into a 1/3 of the line with a ball valve closing off the 2/3 of line running by Jehmco pump.
This way you can tap in additional plumbing and lines if you plan on setting up more tanks.
...Ralph