Pawain, why so rude? Not everyone has those 120s lying about?! Judging from what (s)he wrote:
This makes us think Shannow only has a 105 Powerscroll used on this char, with (at least) 15 Taming skill on ring and/or brace combined? (Or even the Talisman.)
We ourselves also worked up the taming skill to 120 on several tamers, as we felt we got more refusals from pets on our 110 AT Stealth-Tamer. But while we are not 100% sure, it SHOULD not be real skill that matters for that. We transfered pets to starting tamers who jumped to 85 with ring, brace and tali, and could accept Stygian Drakes. So we feel training an animal might work similarly.
Shannow, you getting that warning makes us think the taming requirement jumps to 108 on the first upgrade, though we haven't gotten round to train a Hell Hound yet. (The 5 we have on one tamer are for their Pack instinct.) We'd say try to get your taming at least to 110, so you can control all trained pets. (If you play on Europa, we have one for you.) Hellhounds should be 1-4 indeed, not sure why UO Guide says 2-4. Maybe they confused them with the large Hell Cats? (That seem to miss entirely in their list of tameables?)
Unfortunately Imps have been changed for the worse, making them nearly irrelevant, starting at 3 slots... They used to be 2 slots before one could train them.