No, iPhone to iPad tethering will not provide the iPad with a GPS position.
OzRunways works by “asking” the iPad location services for an accurate position. If the iPad decides the position information it is receiving is not enough, it will not pass the position to the OzRunways app.
When the position is being provided by a GPS inside the iPad, this signal will be of high quality and rapidly updated, meaning OzRunways can use it to display position information. But, when you are tethering to a phone, the position information is sent sporadically in between all the other tasks happening on your device (like sharing the internet). The data signal is very poor and will be insufficient to provide a continuous position to the iPad.
Be aware that using a 'tethered' GPS signal from your phone will give 'intermittent' position updates (the position will update momentarily and the aeroplane 'present position' will appear on the map). At face value this can make people think tethering for a position signal is going to work. It won't though, and the position will drop back out in a few moments, especially if you start moving. Tethered position data is simply not accurate enough to be useable by OzRunways (you may see your 'position' pop up momentarily though it wont be useable).
If you have a wifi only iPad, to get a GPS position you will need a dedicated external GPS for iPad. See companies like XGPS, Bad Elf etc from your local pilot shop, or by using an ADS-B receiver with internal GPS such as SkyEcho2.