100% yes you can. Just because someone has a six pack it doesn't mean the necessarily mean they have a strong core. Having a six pack comes down to several things such as a persons genetics and also their nutrition.
Having visible abdominal largely dependent on the body fat percentage that you have. If you have a higher percentage you are less likely to see them as there will be a layer of fat which is covering them, whereas if you have a lower body fat percentage of somewhere in the region of 1-15% then you are more likely to be able to see.
On the flip side; your core may be as strong as a wall and you may even find the most challenging or core exercises reasonably comfortable yet you are still unable to see six pack, this is mainly down to the body fat percentage.
Finally, everyone's bodies are different, people inherit different genetics and different muscle structures so some people won't be able to ever physically get a six pack. Their genetics may mean that they can only achieve a four pack or maybe even a two whereas some can achieve a six or an eight. Unfortunately there isn't much you can do about that as that is how your body is out together. I hope this has cleared a few myths up about six packs and core strength.