To be specific, you're talking about the Rules of Conduct, where players are told, "You will not exploit any bug....You will not intentionally use or share any bug....You will not directly or indirectly communicate the existence of any such bug," etc. There's no requirement, however, that something must be "seen" by any of UO's staff. Accusations and banning are at their discretion, which is necessary. Otherwise, cheaters would have the excuse "But you didn't see me do _____," and they couldn't be banned based on examining things like server logs or item IDs. When the entire MDK guild was banned, I didn't personally know a soul who shed a tear. Guilt by association was just fine, considering all the exploits and harassment that guild was known for, and that members could have resigned any time. A couple of my friends joined a certain guild, whose first rule was to download the speedhack program of the time.
That said, you should have no doubt that I have no doubt about who's cheated. My first house was hijacked by someone who swung a halberd every half second, flatly impossible in 1998. In 1999 when I fought a certain person for the first time (initials ME, a well-known Sonoma PvPer who never could keep friends or allies for long), he was moving so fast that he flickered all around my screen. Yet another who I fought several times wouldn't have had a prayer without the exploit to cast Mana Vampire without losing mana. This person was so infamous that one of my friends sent a mass ICQ one night, "____ is at the ____ spawn in T2A, everyone needs to page so a GM can finally go after this cheater." Back in the YMCA days, I got smoked by a couple of notorious griefers who were using the "sphere effect" or similar, creating such a high weapon skill that I couldn't land a hit, but they could hit anyone every time. I've chased one of Sonoma's most infamous PKs, presumably named after a South American country (misspelled), when he killed a friend and used UOE's "ghostwalk" to escape -- this was in 1998 before there was any stealth. My anti character had high tracking, and I could track him to the very spot where he was sitting, just not see or reveal him.
Need I mention more? If you knew who I am, and perhaps you can guess, you would absolutely agree that I know who was cheating. It isn't an accusation I make lightly.
Regarding speed, remember that some monsters move very fast, especially if you recall out and return to that subserver. They'll make a fast beeline for your character. When it comes to player speed, time and time again it's been pointed out that there's a hard cap in UO, above which a faster Internet connection and PC don't make a difference. I've heard the excuses "I have a better connection" or "I have a better computer," which means the speedhacker is a liar too. As a matter of disclosure, I ping 40 ms to the West Coast shards with a broadband connection of 29 Mb/s down and 6 Mb/s up, but there's still the speed cap. You might have been at the old Fight Night where I got robbed, and though it couldn't be "proven," it was obvious this person couldn't be legitimate in his speed. Storm O'Neal and I actually caught him one night thanks to a well-timed bola, and even that was lucky. I've chased after speedhackers who, my tracking skill showed, were stealthing faster than I could run on a mount.
I've paged countless times. I've said to a GM that it's so obvious someone was ____ if only the GM would take 30 seconds to watch. Almost every time I'd get a response that they'd look into it, and one GM threatened to ban me if I paged one more time. How's that for a strong stance against exploiters? And that was a dozen years ago, when it really mattered.