You would not normally use the coordinates from the GPX data as they could be 10s of metre out, even if the local datum is correct. If the local datum is wrong, e.g. because local mapping was based on satellite imagery which had not be fully georeferenced, you would also need to take account of the systematic offsets in the area.

You need to place the hydrants in the correct relationship to adjacent objects.

Also, you need to chech whether they are already mapped.