If you're mainly doing normal dungeons, it works fine and you don't even have to optimize for it. All of my characters are hybrids of some capacity, and my warden is a dd/healer who is pretty much what you are thinking of doing except she's bow-bow. Pretty sure she could do some of the veteran dungeons and DLC dungeons as well without needing to optimize anything too, I just don't care enough to try. Things you'll have at your disposal:

1. Soothing Spores (stam). Keep in mind you want to be relatively close to your team to get the most heal out of this ability.
2. Leeching Vines (mag). Mainly use this for the minor lifesteal, though there is an alternative you can run instead.
3. Green Lotus (mag). Lets your light and heavy attacks heal. The heal can be quite substantial.
4. Healing Thicket (ult). Cheap AoE healing ultimate that persists if they leave the area (and they will).
5. Accelerated Growth (passive). Gives major mending when you heal someone under 40% health.
6. Emerald Moss (passive). Will give you a bit of a healing boost for slotting green balance abilities.
7. Maturation (passive). Increase max health of allies by 10% when you heal them, which is very useful.
8. Expansive Frost Cloak (mag). Don't always count on allies bringing their own major resolve and major ward.
9. Sanguine Altar (mag). Alternative to leeching vines that will apply minor lifesteal and offers a healing synergy.
10. Bone Surge (stam). Grant allies a decent damage shield that can also boost their healing received.
11. Echoing Vigor (stam). Large AoE heal that will complement soothing spores.
12. Reviving Barrier (ult). Alternative to healing thicket for protection and healing of allies.

The main thing you will be missing is the ability to help allies with resource recovery. Honestly, that's not a big deal if you're just doing normal dungeons and a few vet dungeons. It's a pretty fun play style.

Honestly, I wouldn't worry too much about bringing what elitist competitive types would want to the table, because you're never going to hit that with a Warden stamina healer. For that crowd, it's basically "run this cookie cutter setup or GTFO" anyway, even though playing like this will work for most content. What I like about it is that I get to stick with what makes sense to my character while still being effective and fun to play. She has pretty respectable damage output this way too, which for most normal dungeons can help do a run faster than having a dedicated healer. Depends on the group you get, though, as with many things with 4-person content.

One thing to keep in mind is that you won't have a crutch heal. By "crutch heal" I mean a brainless easy heal where you can push a button and fix who needs fixing without needing to think, aim, or be strategic. All of your heals require positioning to hit your targets. It's part of why having lifesteal is useful, as it helps mitigate that problem a bit. Green lotus is also super useful for that same reason, because it's the closest you have to a "crutch heal." Personally I find it more engaging, but it does mean you have to pay attention more.