Hi, ReMz,
I suspect Jessica's referring to those adorable little dwarf aquatic frogs, which are often kept in with bettas.
The only issues with them that I can think of offhand are that they sometimes need direct feeding, as they are said to be rather slow and tend not to notice food passing nearby or look for any until after it's eaten by other inhabitants, and are apparently escape artists, so it's best to have netting or some such thing securely fitted over any holes in the tank canopy - including tiny ones for air hoses which people thought they couldn't fit through...
But they are supposed to do well with bettas, if fed by 'hand' in the case of slower frogs, as apparently many of them are.
Jessica.M, this is probably stuff you know but I thought I'd mention a few points to consider, just in case.
Cories and otos are both sociable creatures which aren't very happy or at their best on their own.
You'll note ReMz recommended a pair in either case, and one hears from fanciers that three is minimal.
Too often, if algae isn't available, otos may prefer starvation to spirulina tablets or offered vegetables, so an established tank with existing (if not necessarily visible) algae is generally recommended, and a planted tank specifically, for a variety of reasons, and I've heard 1 oto per 5 gallons is best, to assure a steady supply of algae.
Doesn't mean people haven't kept them in a variety of conditions and they haven't survived in many cases, but while some are tank bred, many otos sold have apparently often been captured from the wild through the use of toxic chemicals and other damaging methods, leaving them with a reputation for being delicate often verified by all-too-frequent deaths.
2 otos probably would be fine, but I wanted to mention this, as I know mine have refused to eat for lengthy periods because they were being moved and no algae was available.
If it's a new tank set-up with little or no algae yet formed, you'll have to hope they will eat something you can easily provide, which they might.
But there's an unfortunately good chance that any otos bought may arrive half-starved and damaged/depleted from the capture and shipping to receive no food at the pet store, as typically no algae is left in sales tanks, and may not recognise anything you have as food, if no algae is available.
Panda and other small cories aren't as small as pygmies, but may be a safer bet if the betta's temperament isn't known - pygmies tend to swim around midlevel and are small enough to be easily injured.
Again, pygmies are probably fine and a MUCH better size for such a small area, not to mention the most adorable things going.
I know I do have a betta I wouldn't put them in with, although my others are, or probably would be, fine with them.
A divided 10 gal. is far more stable and forgiving than 2 five gallon tanks would be, both regarding water quality and temperature.
But there's the same lack of 'get-away room' in both cases - not to mention restricted roaming area - actually less in any standard ten gallon divided in half, as they're taller with relatively less ground/surface space.
In a heavily planted tank with nooks and crannies in which a smaller fish cannot be trapped (i.e., more than one exit/escape route) more options - and fewer tensions - are possible - as the betta is more likely to become bored and to notice other fish in such a smaller area which has little cover or swim-through activity - and there'll be nowhere for the fish to go if the betta becomes persistent or outright aggressive.
Most fish can easily outswim the average betta, but a persistent chase by a slower fish would be stressful and wearing, at the least.
Otos and cories, like plecs, are generally accepted by bettas with little or no problem, but betas are very individual and it's hard to generalize.
But personally, I'd want to have some kind of a back-up ready, just in case.