Hi there,
I'm not sure there is enough information here to suggest that he would be right for an ADHD diagnosis or assessment. I would hold off thinking about that until you have things in place consistently then think about it if nothing improves. It might be worth going to the GP to determine that there are no underlying health conditions leading to accidents if you haven't already done so.
With regards to toiletting, It would be useful to know what has already been tried to support with toilet training? Does he use the potty at home willingly? Does he need to be reminded to use it? and what he is given as a reward when he uses the potty? Reward charts- i.e. getting a special sticker and putting it on a chart (whilst on the potty) and praise whilst he is on the potty will help him associate using it with praise and positivity making him want to use it more.
Consistency is really important here whilst he is learning and this needs to happen at home and in daycare, they need to take some responsibility or supporting him too. He needs to be prompted to use the toilet or potty fairly regularly even without asking to use it (ideally the same potty in daycare as at home). This way he will develop an association and it is more likely to end up in the potty/toilet than on him. When there is something left in the toilet he should get loads of praise and rewarded with the same sticker chart as at home (or whatever else you use). I also wonder how they are responding to him when he does have an accident. If he is being told 'no' or 'thats bad' when he does have an accident it's likely that he will begin to find it an aversive experience, making him even less likely to tell someone he needs the toilet. If he does have an accident it should not be made in to a big song and dance, do not comment on it (unless he is distressed and crying, in which case he needs comfort), he should be supported to change himself (in the bathroom where the toilet/potty is kept) and then directed back to the activity he was doing before.
I am unsure from your post whether he minds using the potty or if he might be a bit reluctant, or if he even understands fully what it is for. I have used loads of story books to help children understanding the toilet- 'poo goes to poo land' is particularly good for children who are scared - if you google it will come up. There are lots of different ones available online so you can see what is likely to suit him best. On top of this to help his understanding you could do some role play with his toys- so for example when playing you can say 'Ooh I think teddy needs the toilet- what should he do?' Then support him to take teddy/ another toy to the toilet, talking about how clever teddy is. When he starts doing this you can ask him how teddy knows he needs the toilet and then teach him about feeling it in his tummy.
In terms of behaviour at daycare in order to support him you could do with working out what he gets from hitting out- is it access to toys or objects? He doesn't understand not to do that? He needs interaction from them? He wants them to get away from him? It may take a while to work out and initially it may not be clear, but once you understand this you can find a way to help him show more appropriate behaviours to get his needs met. Also think about the environment- is it just happening at daycare?
Sorry for the lengthy post I hope this gives some new ideas- it can be hard to potty train!
Well, those are a few signs of ADHD, but would need a lot more info. However, your local school district might be able to help. They will do testing. Most schools have found that it is better to get kids into programs early rather then later. So try calling up your local school district. It is possible that your day care might also be able to give you some advice?