You can only have one minor and one major buff (for the same type) active at the same time, potions are also affected by this mechanic.
Crit surge and Rally both give a major weapon damage buff so they wont stack. I think both effects will work, so healing on crits (from crit surge) and hot (from rally) but only the last applied buff will be active.
To be more precise, the major buff "brutality" will not stack from both spells but you can have both of the healing effects, i.e. healing x amount every 2 seconds from momentum and healing for damage caused from surge.
I actually use Forward Momentum, Power Surge, Siphon, Degeneration, and Mutagen all together. Awards a ton of self healing while attacking.
Gar'Sol the Wanderer VR14 Khajiit Sorcerer Spellblade