There is a huge difference between a raw Flush Draw or OESD and one with added equity in the form of a combo draw.
A combo draw could be something like a flush draw + 2 overcards to the flop, or a OESD + overcards, or Combo Flush + Gutshot etc.
If you are facing an All-in on the flop, you will likely always be up against 1 pair or better. So you want your draw to have at least 50% equity against a single pair, which many combo draws will have. Raw Flush and Straight draws without added outs will only have around 30%-35% equity, so unless you are getting very good odds on your call (opponent didnt have that much too shove) this should almost always be a fold imo.
If your estimated equity is above 50% you should always consider the call. Your no-pair hand is statistically ahead in these situations, and you should be even more inclined to do so if your drawing to the nuts.
Keep in mind, its always better to do the pushing, then doing the calling with draws.
When you do call, just remember, even the best combo draws are pretty much coin flips against made hands. Weak flush draws and OESD are around 35%.