I've never had any issues sending progressive footage (that's been converted to interlaced) to news stations before. It has a different look than interlaced but they've never bounced it because of any incompatibility. I'd say as long as it still looks good then go for it.
The difference between 25Fps interlace and 25 progressive is merely a temporal difference how a single frame is captured and transmitted/displayed.
Interlaced only means that 50 half resolution frames are send in a serial way. First the odd lines (1-3-5..)of frame one, then the even lines (2-4-6...), repeat for the next frame. So an interlace signal has a temporal difference between field one and two for a single frame. Progressive capture/display shoots a frame as a whole with all lines at once (bit more complicated than that but this is the principle)
So when you shoot progressive your 25 frames just get transmitted/displayed at a rate of 50 fields per second, but every 2 fields are the same frame in a temporal sense. Technically this isn't any difference to an interlaced captured image, it just looks different because of the way time is captured.
When you shoot 50 fps progressive and convert this to 25 interlace then it really depends how the conversion is done. Either take every 2nd frame and use those to make up your 25 FPS, then divide them in 2 temporal equal fields. The result would be same as shooting 25 progressive. But you could also take half the lines of frame one and combine this with half the lines of frame two to a new frame 1 in your 25 FPS sequence. The result will be the same temporal different 50 fields 25 FPS interlace produces.
So in summary technically there is nor problem whatsoever to convert either 25 FPS or 50 FPS into 25 FPS interlaced. The resulting clip is technically 100% acceptable. The difference is only the look. Interlaced with 50 fields of temporal resolution looks like 'TV' and 25 FPS progressive more like 'Film'. It effects things like pans where progressive stutters more because it captures less moments in time.
Hope that helps a little
PS you might ask why the heck is there in a difference in the first place? Interlace only exists because of the technical difficulties to transmit images electronically at the time television was invented. Europe TV is 25 FPS because Europe works on 50 Hz power (American is 30 FPS because they 60 Hz power) Technically the simples clock to use is the freq of the power grid = 50 Hz. But it would have taken too much bandwidth to transmit 50 full frames. The human eye stops seeing single frames above 20 FPS (I think) so film before used 24. Knowing this TV guys decided 25 would be enough. So they just transmitted half the size every 50th cycle (50 Hz). The total lines per frame was then limited buy how much information they could send over the available bandwidth. This is a very simplified explanation, but I always like to understand the background of things, to understand why they work the way they do
If you are going to do more work for broadcast the Intensity Shuttle might be worth buying. It is best to see your editing process on broadcast compliant equipment. The Intensity Shuttle works with FCPX but not as good as it should. Motion graphics look better at 1080i VS 1080 30P. The color space for broadcast will be slightly different as will the composition because of the over-scan area.