I would think it is as bittrex doesn't change your address once generated, at least it hasn't in my 6 month experience. I would still suggest not to for the risk of them changing it at any given time, since you do not own the private key to that address. Sending VTC is practically free, so the smart thing would be to mine against your own wallet.

So you're saying you were pointing to stratum+tcp://vtc.poolmining.org:3096 before and the stats were not updating? This should not happen, at least it didn't happen for my miners.

In PPLNS, some shares get carried over to the next block even if a real block is found. Basically your window of eligible shares constantly "travels" across an imaginary stack of shares. A new share always pushes out an older share that falls beyond the window.

When the next block is found.

Possibly. It's also possible that we find it any minute. Mining is a game of probabilities and statistics. You always have a chance to find a block at any given time. You never have 0 probability if you are mining. The probability increases with your hashrate. On average though with the current hash rates, we should find it every 16-17 days. 

Ethereum has a high orphan/uncle rate, probably the highest of the all blockchains, especially due to the gas limit increase and relatively low difficulty leading to short block times.

Someone else found the actual correct block, our block was correct as well, it's just that we mathematically found just after the other accepted block. In other words, someone else beat us in calculating the mathematical equation and propagating it to the network first. We still did the right job, we just did it slightly later. In other blockchains, such uncles are not rewarded and are orphaned. Lucky for the miners of Ethereum is that they get a partial reward nonetheless.

It depends on how you look at it. The block reward is still the same no matter what, it's not that you are getting less ether for the block, it's just that you are wasting more electricity for it. So you are getting less ethers for Kilowatt/h, or less ethers per a unit of time. It's like this at every pool. Sometimes you find the block faster than the expected time, sometimes it takes longer. At coinfoundry, most blocks are found faster on average and we end up earning more than at other larger pools, where the time to find a block averages out more at 100% expected time. For Ethereum over here at coinfoundry, we are at 67% average, it will go worse a bit now with the due block, but still better than mining at a large pool.

Just variance. You can't have <100% effort all the time. Eventually you can hit a few >100% efforts in a row as well.

We are probably over 100% effort already, so the block is due. It might come anytime, but like Opa said, it's also possible we might have to wait another 2 weeks.