This is a long story so I'll keep it short.

I was on EK229 from DXB-SEA on July 30 traveling Y and the flight departed late which caused me to miss my onward connection to YEG. Emirates without telling me rebooked me along with nine other passengers who were in the same boat to the same flight departing the following day - which was a full 24h later.

There was no Emirates agent to speak to at the airport and multiple calls to the call center were useless, I was directed to simply talk to an emirates agent at the airport and when I told them there was no agent they told me to send an email in.

So I ended up having to book a hotel and buy meals for myself which wasn't cheap at all.

I sent an email in to emirates customer affairs department complaining and asking for compensation and got a response saying too bad so sad we aren't giving you anything, and they are refusing to even to cover the cost of the hotel and food which I had to pay out of pocket.

Would the fact Emirates moved my flight to the next day (as they clearly knew the connection would be missed) be considered involuntary bumping so I could claim compensation under the US rules?

Any other suggestions to get my costs out of Emirates?

I understand you were booked until YEG. Your story is surprising : EK is usually good at handling missed connections. Keep your receipts and file a complaint.
What did the other 9 pax do ? I guess you moved together.

To answer your direct question, no you were not involuntarily denied boarding. Under US law, that only occurs when you are at the boarding gate in time for your flight and are denied boarding based on an oversell. Clearly you were neither.

As to having your expenses covered, you are at the mercy of EK. There is no law requiring EK to cover your costs. Those should be submitted your travel insurance which I would hope would pay up pretty quickly as this seems to be a fairly clearcut travel interruption.

Both flights on 1 ticket (through fare?) or SEA-YEG on a separate ticket?

All booked on one ticket and all though emirates. Round trip YEG-SEA-DXB then DXB-SEA-YEG.

Seems strange. I have flown multiple times in a similar way to the UK connecting to Flybe (all booked on the emirates website )

The one time I missed my flight due to late arrival of the EK flight , I was given a hotel room and meal vouchers at Manchester . (EU compensation did not apply as it was a flight to the UK by a non EU carrier). However they still did it.

The flybe flight from MAN was operated on a EK flight number so I don't know if that helped??

As a through booking, unless there was no other option to get to YEG, Emirates is liable under Article 19 of the Montreal Convention to pay for the costs of hotels et al

There seem to be plenty of flights between SEA and YEG so would see the exception unlikely to be applicable

Did you ask the airline for reimbursement of the expenses incurred or for compensation?

There is no entitlement to compensation, but there is entitlement to reimbursement of expenses

I asked for reimbursement of my expenses - Hotel and food. So far I've been told to pound sand. I was told had I called in they would have assisted which did not happen during the multiple times I called in when this was going on.

Everyone in Emirates seems to pass the buck.

Try tweet at @EmiratesSupport they're generally kind of helpful

In which case, I would simply put in a claim against the local Ek office through a small claims court

Last try is a CEO email, then off to court I will go.