I don't know about the hagen fixtures, but I have several 36" coralife t-5 (21 watts x 2) fixtures. Those were actually the only thing I could find that would work for me on two of my tanks because they're on a counter with cabinets above them, and if I got anything taller I wouldn't be able to access the cabinets. Don't worry about the bulbs being 28.25"... Even regular everyday fluorescent bulbs are not the length they say they are. I just measured a regular 36" bulb, and it's 35" not including the pins, or 35 3/8" including the pins. You just need to look for 30" t-5 normal output bulbs. If the fixtures will be sitting right on top of the tank, you would need one at the front and one at the back to cover the tank. But, 2x 2.25" lights would only leave a 7.5" gap for the MH to go through. (29 gallon tanks are just 12" front to back though, right?) I don't have a GE 9325K to compare it to, but from pictures I've seen, it seems that using the coralife colormax bulbs as a supplement to daylight bulbs has a similar effect to the GE's. I really like the colormax bulbs (not by themselves though!), and coralife does make 30" t-5 bulbs for that fixture.
All that said... I'm a little concerned that 150 watts of MH on a 29 gallon is already "living on the edge". Adding another 36 watts might not be a good thing. Of course, that's not coming from personal experience; I just thought I'd mention the possibility. If you're not too set on keeping the MH (I don't know if I could give it up if I had one...), there are other options that would cost about the same or less than two supplemental light fixtures + bulbs.
All that said... I'm a little concerned that 150 watts of MH on a 29 gallon is already "living on the edge". Adding another 36 watts might not be a good thing. Of course, that's not coming from personal experience; I just thought I'd mention the possibility. If you're not too set on keeping the MH (I don't know if I could give it up if I had one...), there are other options that would cost about the same or less than two supplemental light fixtures + bulbs.