Installing Stewart Turner 3 bar pump

Hi
I am finally getting round to installing a 3 bar Monsoon pump that I have had in the garage for a couple of years and I would like to use it to pump all the hot water in my bungalow and both hot and cold to two showers.
The hot water tank has a surrey flange already fitted to it so I can use the 90 degree outlet from that to supply the hot.
Is it ok to use the top outlet from the surrey flange as a vent only as i do not want to supply anywhere with hot without being pumped ?

yes

Is there a possibility of it sucking air down the top outlet if used solely as a vent pipe?

no reason why as its a vent its still full of water.no different from putting the pump straight onto the vertical pipe when the vent is above.
shower pumps only pump they don't suck.