I assume WHM since you mention enmity:

1.) While telling us does help a bit, a good tank (solo or not) won't lose hate unless the WHM refuses to Shroud. It's honestly probably better for the tank to have a macro to signify when the healer is starting to reach that threshold where it'll overtake the tank. This is only true if there is a lot of Medica 2ing going on as that can get ridiculous quickly. Shouldn't be much different from when you heal Titan HM, except for all the split damage - but it's controlled split damage for the most part.

2.) Nope! SS is low cost for a relatively great reward. Other than Flash, the only option a PLD has for using his MP is SS and if the PLD were to actually need MP back, they simply have to RB combo once or twice. Basically, don't panic and let them do what they need to do to mitigate what they've got to mitigate - you'll see this a lot in T5 if you haven't done it already.

Just remember - Shroud is your friend!