While we wont know until it hits lama/live, no other core in the game works like that and I see no reason why this should be any different. So I think its safe to assume theyll stack.
In a dev post
here, in response to asking for clarification on cores stacking, the implication was that they do unless its stated otherwise (through the use of "now" to indicate replacement rather than stacking). Which is why I feel its safe per above.
Given how cheap that 30 amp (and 30 hp for that matter, as they are generally 5 hp / AP, not 10) is, it certainly seems like a concern. Many builds can afford to toss 3 AP into 3 trees for 30 amp, because many builds will have 99% of their AP tied up in 2-3 class trees. Its pretty rare for a build to need all 6 class trees so badly they cannot adjust at all (and such builds generally arent the kind for which 30 amp is going to make a difference, once you get that complicated/precise theyre generally performing well regardless).
Another way of looking at it is: Even taking 1-2 trees it is superior to other options. Humans can spend 17 AP to get 30 amp in racial, or anyone with 1 barb lvl can spend 3 ap for the same. Getting the first human 10 amp costs 3 AP, for anyone with barb levels its 1 AP. Definite concerns there. Not saying its broken or anything (as Ive said multiple times, I really dont think the healing amp is all that powerful... people are still thinking in terms of live now, not in terms of the new formula and how everything stacks up in that environment). Just dont want to see something get in, then get nerfed over some combination, etc.