If you open a demo account with a spread betting broker, you'll be able to see for yourself the markets that are open in the evenings. Trading around a full time job has more to do with the trader you are - i.e. day, swing or position trader - than it does choice of market. If you're a swing or position trader - then you can trade pretty much any market by placing 'set 'n forget' pending limit and stop orders. If you want to day trade, then yes, your choice of market will be limited to the hours you're able to spend in front of the screen.
Here is a nice market hours converter: http://www.forexmarkethours.com/
Depending on what evening means to you then you may be able to trade the second half of US and few hours of sydney.
Set and forget as well as automated strategies may work well in your case.
The short answer is yes. However, the question implies that you don't understand fully the nature of spread betting products.
Take a look at the product details page on IG. As you can see, the FTSE is 'open' and can be traded more or less around the clock. The same will apply to currencies. This is because with a spread betting broker, you are trading their prices, which are based on the underlying market, but are not the same as the underlying market. This explains why to can trade the FTSE long after the London Stock Exchange shuts up shop at 4.30pm. You may be wondering what the SB firms base their prices on if the underlying cash index is closed? The answer is the futures. This applies to all equity indices (i.e. Dow and Dax etc.) not just the FTSE.