Roninhood, your numbers for health regen are not accurate. For example, my 39 Nord DK only has one point in the health regen passive (so +5%) and has no gear in +health regen and he is softcapped at +39hp per tick. Whether you have the passive or not, you still get natural regen that increases based on your level. The passive merely augments that natural regen. Natural level up regen seems to be +14 mp, +14 stam, and +8hp per tick for every 10 levels (rough estimates), but adding to your max amount tends to boost it as well.
So at level 50 you're talking about +50hp per tick for an Imperial versus +58 per tick for a race with +15% regen by my estimates. Not a gamechanger.
A tank's primary role is in a group with a healer, so his magicka and stamina regen are more important as they affect his ability to maintain agro, help CC, and mitigate with blocking. In my experience though, if you get all the 1h/shield passives, you only use a lot of stamina blocking in large AoE situations, so how important stamina regen is on the hierarchy of needs falls more towards skill activation than damage mitigation. Also, the third skill (Inner Fire) on the undaunted line is a ranged taunt using magicka which is a nice taunting alternative to the 1h/shield pierce armor for when you're low on stamina.
Anyways, if you're talking super long sustained fights, the redguard has to be a favorite based on their stamina regen passive or the Argonian for their healing received bonus and potion effectiveness. But personally, for tough group or raid dungeon content (i.e. where a tank is most needed), or for AvA (where alpha defense and EHP are king if GW2 is any indication), I'll take the large max health and stamina passives that Imperials offer.