A 5 yr old boy should be able to wipe himself, and at least mostly hit a target. Yes, they will have occasional accidents, or not do the greatest job still, but they should be at least fairly proficient. And a 5 yr old should be able to take a bath & brush their own teeth, though they still need supervision and possibly some help. Ie-my BS had me come and help him rinse his hair in the tub until he was like 6-7 because he just couldn't seem to get the soap out.
You may just need to set DH down and tell him you are concerned about it, and that the other kids (I'm assuming he goes to kindergarten) will start picking on him or not want to be his friend because no one wants to hang out with the "smelly" kid.
One thing I've heard mentioned for aim is putting a cheerio or fruit loop in the toilet and telling them to try to hit it. Boys are inherently kind of gross and like to do that sort of thing, lol.
Another thing I started doing when the boys don't do so well on the aiming thing is...Guess who gets to clean it and the toilet up! Even at 5 he can be handed cleaner and paper towels and told to wipe it up. They got better fast.

Your SS should have a grasp of how to bathe himself. Not saying he should be unsupervised, but he should be doing it on his own. I would just flat out tell your DH to smell SS. Thats what I did. I couldn't take it anymore.

When DH was going through his custody battle, we put a fake tattoo on SS's leg before he went home to BM (on a Sunday), when he came over on Friday, it looked like it had been untouched. Maybe try that approach if you don't want to flat out tell him, then you can say, wow it doesn't look like he's bathed all week. And then maybe bring up the fact that you have noticed an odor when he comes over. That may be an easier way to break it to him?

"If I turn into another, Dig me up from under what is covering the better part of me" -Incubus

Try having to talk to your FH about his then 9 year old son smelling like poop! Maybe I'm just sensitive to smell and am about anal about my own hygiene etc. but the boy really did smell like he hadn't wiped after number 2 and was sweaty. FH agreed and asked SS to shower (I wasn't in the room when they talked). Of course, the response was denial of needing to shower and crying. What is it about boys and their aversion to taking showers/baths? He sleeps with the dog every night with his door closed so his room and blankets smell of concentrated dog. It's gross... yet he likes it that way.

My son is 5 and has started bathing himself. He loves being clean, so it was really easy to transition from me bathing him to him bathing himself.

His Dad or I will put the shampoo in his hair (if not, the whole bottle would get used) and he does the work and then he washing his body with soap and rinses off. I do come in to check on him every couple minutes, just to make sure he is progressing and not wasting water.

He is getting good at it and is very proud of the accomplishment! If anything my son is thinking he is super cool and a big boy since he knows how now.

He is very good when it comes to going to the bathroom, he doesn't pee on the floor or the rim and he will attempt to wipe himself, but is freaked out at the thought of having "doodie" on his hands, so he will try first and then his Dad or I will help him to make sure he is clean.

I don't sugar coat it either.... SD11 never 'remembers' to put on deoderant and OMG sometimes she REEKS to high heaven when she comes over. I make no bones about telling her to her face that she STINKS and better hit the shower the second we get home. I have zero tolerance for b.o. of any kind due to laziness. (Working outside all day in 90+ degree heat gets a pass IF you shower immediately without prompting.. haha) She's horrible about washing her hair and rinsing properly and often has greasy hair or dandruff so you know what I do? I make her put her head in the kitchen sink and I SCRUB her head. I mean scrub it hard too. I figure I will eventually shame her into proper hygeine if nothing else!

Directness with DH is your best bet, I agree. My SS10 often smells, he will be picked up by FH from school on Friday, dirty (greasy hair, dirt under his nails, and BO), and never follow FH's directives to shower. He hadn't showered since Thursday morning and didn't shower then until Sunday evening. I don't understand-- his parents are not uneducated. His BM has multiple graduate degrees and is a published author. My FH (who is a professor) doesn't really follow through with his son and his son has no responsibilities in our home--- so it doesn't surprise me that he allows his son to stay dirty.
I have just started saying to FH directly that his son is dirty, he has BO, dirt under his nails, and is gross. He is also a kid that eats with his hands a lot, and I have real difficulty watching him eat with hands that are dirty and have dirt under the nails. But I shouldn't expect any different since neither parent enforces him being clean!