Victor,
Same guidance as all Aruba APs in terms of capacity - recommended 150 associated users per radio/300 per AP. 50 concurrent users per radio/100 per AP. Max is 255 per radio / 510 per AP.
AP175 hardware is functionally equivalent to an AP105.
Only thing to be careful of outdoors is that farther clients may be connecting at lower rates due to distance or multipath environment. This may result in lower overall channel capacity as compared with indoor operation.