It is the same ping. I don't know why you get packet loss with check-host-alive, it's possible it's just the coincidence. Check-host-alive is not performed very often, so have trust in check_ping. Maybe there was some loss also with check_ping but you've missed them, because it is run more often, as I've already said, and every new check overrides the old ones.
You can check the log of Nagios and grep all check_ping services for every host and see if there was any with packet loss to be sure that none ended up with packet loss.
But, anyway, nothing to worry about, as far as I can see.