Mine was painted by a previous owner. You can see the odd brush mark if you look closely, but as you say, a lot cheaper than a retube. I don't know what product was used.
When you say rough and sticky, are you sure that's not where some glued item has been removed?! I'd be careful if you have any doubts about the integrity of the tubes, maybe use some patches first to tidy up first?
IBS also do Hypalon paint - take a look at www.ibs-boats.com
You have to download the PDF catalogue and price list. It's £25.69 / litre which covers 6sq m According to my calculations you would need 3 tins.
If it can be sprayed then of course you'd get a better finish.
Some of the retubing pros might have a view on this as well.